Kim Gu was born on August 29 (Lunar Calendar July 11), 1876 in Teot-gol (텃골), Baek-un-bang (백운방), Haeju (해주; 海州), South Hwanghae Province, Korea, the only son of a poor farmer Kim Soon Young (김순영) and his wife Kwak Nack Won (곽낙원). His name at birth was Kim Changahm (김창암; 金昌巖). When he was nine years old, he started to study Chinese classic texts such as Zizhi Tongjian (자치통감; 資治通鑒), and Great Learning (대학; 大學) at local seodangs.

At the age of 16, Kim applied for the Gwageo (Imperial Examination) of Joseon but failed. After that, he joined the Donghak (동학; 東學) movement in 1893 and changed his name to Kim Changsoo (김창수; 金昌洙). As the organization grew rapidly, he was appointed the district leader of Palbong (팔봉) at the age of 17 and led hundreds of subordinates. Kim commanded a Donghak army regiment in the 1894 Donghak Peasant Revolution. Following the instruction of Donghak leader Choi Si Hyung (최 시형), Kim Gu's troops stormed the Haeju fort in Hwanghae-do, but the army was eventually defeated by governmental forces. After that, Kim Gu was defeated by his companion, Lee Dong-yeop (이동엽) in the turf war of Donghak’s organization. Thereafter, General An Tae-hun (안태훈; the father of the An Jung-geun who later killed Ito Hirobumi) of the royal army gave Kim Gu's Donghak rebels a safe pass, but other government troops ignored An's safe pass and attacked them. At 20, with Kim I-eon whom he had met around Yalu River, he attacked the royal army of the Gang-gye fort, supported by the Qing Dynasty's army. However, the attack failed and Kim Gu went into hiding.

On October 8, 1895, Empress Myeongseong (명성황후), the wife of Emperor Gojong (고종) of the Korean Empire was assassinated by a group of Japanese assassins (the Eulmi Incident; 을미사변; 乙未事變). Miura Goro, then Japan's Resident Minister in Korea, was suspected as the mastermind of the assassination. In February 1896, Kim stayed at an inn in Chihapo, Hwanghae Province while traveling to southern regions. There he found a Japanese man named Tsuchida Josuke (土田譲亮), who was disguised as a Korean and concealing a Japanese sword, and killed him believing that he was involved in the assassination of the queen. In his biography 'Baekbeom Ilji' (白凡逸志), Kim describes his motivation at the time as follows:

Since many Japanese go through Chihapo every day, there is no reason for him to disguise as a Korean if he were an ordinary merchant or workman. Could he be Miura or one of his accomplices who killed the queen, fled from Seoul and hiding here? Even if he is not, a Japanese man with a disguise and a sword can do nothing but harm to my country and people. I will revenge for my queen by killing this Japanese man.

– Baekbeom Ilji

The following morning, Kim attacked Tsuchida, took his sword, and killed him with it. The "Report from acting administrator Hagihara Moriichi of Incheon Consulate on the current situation of Incheon" describes Tsuchida as a "commoner from Nagasaki Prefecture" and an "employee of a Nagasaki trader on a business trip". However, this does not prove that Tsuchida was not involved in the assassination of the Empress Myeongseong, as this assassination was carried out not only by Japanese soldiers but also by many Japanese Ronins, as described in the report by Ezo Ishizuka (石塚英藏), the Japanese adviser to the Korean Empire at the time. In addition, Kim stated in 'Baekbeom Ilji' that Tsuchida was concealing a sword and had identification papers that showed him to be a Japanese army lieutenant. Official Japanese interrogation police records from the time also verify the fact that Tsuchida was carrying a sword around.

After the killing, Kim left a hand written document which said "Kim Changsoo from Haeju, Hwanghae Province, killed this Japanese man to revenge the murder of Korean Queen", as documented in Baekbeom Ilji. He waited at his home at Haeju for three months before the police came and arrested him.

Kim was tortured and sentenced to death. According to Baekbeom Ilji, however, many Korean people were sympathetic and admired him for his patriotism and bravery, as shown by the facts that his execution was suspended by order of Emperor Gwangmu, that Korean judicial officials behaved politely to him despite Japanese pressure to execute him promptly, and that influential Koreans at the time (including major merchants of Inchoen) made efforts to rescue him by repeated petitions to Korean Justice Department Officials and by collecting money for his ransom before his scheduled execution date.

In prison, Kim had a chance to read newly published textbooks about western culture and science such as Taesoe Shinsa (태서신사; 泰西新史) and Saegye Jiji (세 계지지; 世界地誌). He was deeply impressed by the strengths of new western science and recognized the importance of education for the Korean people. He started to teach about 100 illiterate prisoners in the prison. The Korean newspaper Hwhangsung Shinbo (황성신보; 皇城新報) reported at the time that Kim Chang Soo changed the Inchoen Prison into a school by teaching prisoners.

In 1898 he broke out of prison and escaped into Magoksa (마곡사; 麻谷寺), a Buddhist temple in Gongju (공주; 公州) , Chungcheong province, and entered the Buddhist priesthood. Kim left the priesthood and returned to Hwanghae a year later, where he devoted himself to the enlightenment and education of the Korean people, founding (장연학교; 長淵學校) and the Yangsan School (양산학교; 楊山學校) in 1907, becoming the principal of the Yangsan School. In 1904, he married Choi Jun Rye (최준례) from Sincheon (신천), Hwanghae Province.

In 1905, the Eulsa Treaty (을 사조약; 乙巳條約) was made between Japan and Korea, making Korea a protectorate of Japan. Kim participated in a mass protest against the treaty in Seoul and presented a memorial to Emperor Gwangmu urging him to withdraw from the treaty. In 1908, Kim joined Shin Min Hoi (신민회, 新民會, New People's Association), a national level underground organization established by Ahn Chang Ho (안창호) for a non violent Korean independence movement.

In 1910, the Japanese colonial government arrested An Myung Geun (안명근; 安明根), a cousin of the An Jung-Geun (안중근; 安重根) who killed Ito Hirobumi, for plotting to assassinate Governor General Terauchi Masatake. Kim, who was a close friend of Ahn, was suspected of being an accomplice and arrested as well. Kim was jailed and severely tortured, but no evidence linking him to the assassination attempt was found and he was released from prison after 3 years.

The Japanese tortured Kim and other suspects. Because of the damage to cartilage due to beating by Japanese in the prison, his left ear was disfigured for life like his calves that were permanently scarred when he was first arrested and tortured for the killing of Tsuchida. At the time, Han Pil Ho (한필호; 韓弼昊), a member of Shin Min Hoi was killed, Shin Suk Choong (신석충; 申錫忠) killed himself, and An Myung Geun tried to commit suicide during the severe interrogation but failed. Kim Gu also tried to kill himself with a self-inflicted injury in his head, but failed.

In prison, Kim changed his name from Kim Changsoo (김창수) to Kim Gu (김구) and adopted the pen name of Baekbeom (백 범, 白凡). Kim stated in his biography that the change of his name symbolized breaking free from Japanese nationality records and that he chose the pen name Baekbeom, which means "ordinary person", hoping every ordinary Korean person would fight for the independence of Korea.

Kim exiled himself to Shanghai, China, in 1919 after a nationwide non-violent resistance movement, known as the March 1st Movement (3.1 운동), which was violently suppressed by the Japanese imperialist government. In Shanghai, Kim joined the Provisional Government of the Republic of Korea (대한민국 임시정부; 大韓民國 臨時政府), which vowed to liberate Korea from Japanese occupation. After serving as the Police Minister, Kim became the president of the Provisional Government of the Republic of Korea in 1927. He was re-elected to the office many times by the Provisional Assembly.

In 1931 he organized a nationalist group, the Korean Patriotic Corps (한인애국단; 韓人愛國團). One of the members, Yoon Bong-Gil (윤 봉길; 尹奉吉), ambushed and eliminated the Japanese military leadership in Shanghai on April 29, 1932. The commander of the Japanese Army and Navy died instantly. Another member, Lee Bong-chang (이봉창; 李奉昌), tried to eliminate the Japanese emperor Hirohito in Tokyo on January 8 of the same year but failed.

After escaping to Chongqing where Chiang Kai-shek's Nationalist Government was established, Kim established the Korean Liberation Army (광복군; 光復軍), commanded by General Ji Cheong-cheon (지청천; 池靑天). When the Pacific War broke out on December 8, 1941, Kim Gu declared war on Japan and Germany and committed the Korean Liberation Army to the Allied side; the Korean Liberation Army took part in warfare in China and Southeast Asia. Kim arranged for the Korean Liberation Army to advance to Korea in 1945 but, days before the departure of the leading unit, the war ended. He returned to Seoul upon the Japanese surrender to the Allies in 1945.

As the division of the newly independent country became obvious, he led a team of former independence activists to Pyongyang to hold unification talks with Kim Il-sung (김일성; 金日成) (who later became the president of North Korea), but failed drastically after being humiliated by Kim Il-Sung.

In 1948, the inaugural National Assembly of South Korea nominated Kim as a candidate for the office of the first president of the Republic. In the election by the National Assembly, Kim was defeated by Lee Seung Man (이승만; 李承晩 - also known as Syngman Rhee), the first president of the provisional government, who had been impeached in 1925 by a vote of 180 - 16. He also lost the election for the vice presidency to Lee Si-yeong (이 시영; 李始榮) by a vote of 133 - 59. Kim himself did not know about his nomination until after the election, and he did not approve the nomination, considering it a ploy to discredit him. Also, Kim would never have participated in the election as he fiercely opposed the establishment of separate governments in North and South Korea.

In June 26 1949, Kim was assassinated by Ahn Doo-hee (안 두희; 安斗熙) in his office. Although some suggest there may have been a right wing conspiracy to assassinate him in which even president Rhee and the CIA could have been involved, no details of the assassination have been revealed. Moreover, Ahn Doo-hee was murdered by a follower of Kim's in 1996 after he allegedly confessed that Kim Chang-ryong (김 창룡; 金昌龍) masterminded the assassination, thus further obscuring the prospect of finding the motive of assassination. Another possible motive for the assassination could have been Kim's connection to the assassination of Song Chin-u (송진우), a leader of the Korean Democratic Party (KDP) who had chosen to work closely with the American military government.

He was posthumously awarded the Republic of Korea Medal of Order of Merit for National Foundation (건국훈장 대한민국장; 建國勳章 大韓民國章), the most prestigious civil decoration in the Republic of Korea. His autobiography, Baekbeomilji (Journal of Baekbeom, 백범일지) is an important source for study of history of Korean independence movement and has been designated as cultural treasure No. 1245 by the Korean government. A steady seller in Korea, the autobiography was first published in 1947 and republished in more than 10 versions in Korea and abroad.

He has been constantly regarded as one of the greatest figures in Korean history. For example, he was voted in a 2004 online poll as the greatest leader after the restoration of Korean independence and in 2005 as the most revered figure by Korean National Assemblymen. In 2007 national surveys, Kim received the most vote as the Korean historic figure whose portrait should be featured in new Korean banknotes that will be issued in 2009. On November 5, 2007, the Bank of Korea, the national central bank of the Republic of Korea, announced the new 100,000 Korean won bill would feature Kim's portrait. However, the issuing of the new bill was delayed indefinitely as of 2009 for an unknown reason.

His second son, Kim Shin (김 신; 金信; 1922-), was a founding member of Republic of Korea Air Force, the Chief of Korean Air Force, a National Assembly person, and the Minister of Transportation, and is currently the Director of Kim Koo Museum and Library. His grandson, Kim Yang (김 양; 金揚 1953-), was appointed as the Korean Consulate General in Shanghai, China in 2005 and as the Minister of Patriots and Veteran Affairs of Korea (국가보훈처; 國家報勳處) in 2008.

At the end of his autobiography Baekbeomilji, Kim expressed his desire with which he carried all his life time:

If god asked me what was my wish, I would reply unhesitatingly, "Korean independence."

If he asked me what was my second wish, I would again answer, "My country's independence."

If he asked me what was my third wish, I would reply in an even louder voice, "My wish is the complete independence of my country Korea."

My fellow brethren. This is my only wish. I have lived seventy years of my life for this wish, am living my life for this wish, and will live my life only to fulfill this wish.

...Recently, some of our brothers have said that they wanted our nation to be a part of a federation of another country. I don't believe this, and if there is really someone who does, I can only say that he is crazy and has lost his mind.

I've studied the ideas of Confucius, Buddha, and Jesus; I respect them as saints, but even if there's a heaven made by them, it's not a nation created by our nation, and I will never take our nation there.

It is because, a nation which shared blood and history is clear, and just like my body can't be another's, the reason that a certain nation can't become another is the same as brothers living in the same house. If two gather and become one, one would be higher and the other lower, so it becomes a basic problem that one orders from above, and the other obeys from below.

And so-called leftists deny the motherland of blood, and say this and that about the so-called motherland of ideology, ignoring brothers of blood-ties, and claims the so-called comrade of ideology and international class of proletariat, and speak as if nationalism is outside the truth.

This is foolish thinking. Philosophies change and theories of politics and economics are only a snap, but a nation's success is everlasting.

...I want our nation to become the most beautiful nation in the world. I do not want our nation to become the richest and the most powerful nation in the world. Because I have felt the pain of being invaded by another nation, I do not want my nation to invade others. It is sufficient that our wealth is such that it makes our lives abundant and our military strength such that it is able to repel others' invasions. The only thing that I desire in infinite quantity is the power of a highly developed culture. This is because the power of culture both makes ourselves happy and gives happiness to others.