In contrast to most of the Nazi leadership, not much beyond basic detail is known about Freisler. He was born in Celle, the son of an engineer, and saw active service during World War I. He was an officer cadet in 1914, and by 1915 he was a Lieutenant and was decorated before becoming a prisoner of war in the Russian Empire in October 1915.

While imprisoned in Russia, Freisler learned Russian, and after the Russian Revolution of 1917, he is said to have developed an interest in Marxism. The Bolsheviks made use of him as a commissar for the camp's food supplies. Another author, H.W. Koch, states that after the Bolshevik Revolution, the prisoner camps in Russia were handed over to German administration, and the title of commissar was merely functional, not political. It is also said, though it is not supported by any contemporaneous documents, that after the prisoner camps were dissolved in 1918, Freisler became a convinced Communist. H.W. Koch rejects this assertion: "Freisler was never a Communist, though in the early days of his NS career [...] he belonged to the NSDAP's left wing". Freisler himself rejected all accusations that he had even tentatively approached the hated enemy, but he could never fully escape the stigma of being a bolshie.

He returned to Germany in 1920 to study law at the University of Jena, becoming a Doctor of Law in 1922. From 1924, he worked as a lawyer in Kassel and also as a city councillor for the Völkisch - Sozialer Block (German, roughly "People's Social Block"), an extreme nationalist splinter party.

In 1928, he married Marion Russegger. Together, they had two sons, Harald and Roland.

Even though the Nazis declared themselves arch-enemies of Marxism, Freisler joined the Nazi Party in July 1925. He registered with the NSDAP as member number 9679. During this period, he served as defense counsel for members of the nascent Party who got into trouble with the law. He was also a delegate to the Prussian Landtag, or state legislature, and later he became a member of the Reichstag.

In 1927, the Gauleiter of Kurhessen, Karl Weinrich, characterized Freisler in the following manner: "Rhetorically Freisler is equal to our best speakers, if not superior. Particularly on the broad masses, he has influence, but thinking people mostly reject him. Party Comrade Freisler is only usable as a speaker. He is unsuitable for any leadership post, since he is an unreliable and moody person."

In February 1933, Freisler was appointed department head in the Prussian Ministry of Justice. He was Secretary of State in the Prussian Ministry of Justice in 1933 – 1934, and in the Reich Ministry of Justice from 1934 – 1942. He represented the latter at the Wannsee Conference (20 January 1942), where he stood in for Minister Franz Schlegelberger, as regarding the detailed plans of the Final Solution, the murder of all European Jews.

Freisler's mastery of legal texts, mental agility and overwhelming verbal force combined well with strict adherence to the party line and the corresponding ideology, so that he became the most feared judge and the personification of the Nazis' "blood justice". Despite his undisputed legal competence, he was never appointed to cabinet. According to Uwe Wesel, this can be attributed to two factors. Firstly, Roland Freisler was regarded as a lone fighter and had no influential patron. Secondly, in the eyes of the Nazi German elite, he was compromised by his brother Oswald's rise to prominence. Oswald Freisler committed an offence against the party line by appearing as the defense counsel in politically significant trials which the Nazis sought to debase for propaganda purposes. In so doing, he wore his Nazi Party badge in a clearly visible way, which made an unambiguous interpretation of the party's position more difficult. Propaganda minister Joseph Goebbels accordingly reproved Roland Freisler and reported the incident to Hitler, who, for his part, decreed the immediate exclusion of Oswald Freisler from the party.

According to Guido Knopp, however, Goebbels was the only Nazi leader well disposed towards Freisler. At a round table discussion in the Führer's headquarters, the Minister of Propaganda proposed his name for the post of Reich Justice Minister when Franz Gürtner died in 1941. Allegedly, Hitler's dismissive retort was: "That old Bolshevik? No!" Uwe Wesel tells a similar story regarding Hitler's remark.

In an article entitled, "The racial - biological task involved in the reform of Juvenile Criminal Law", Freisler, then Secretary of State in the Reich Ministry of Justice, argued that "racially foreign, racially degenerate, racially incurable or seriously defective juveniles" should be sent to juvenile centres or correctional education centres and be segregated from those who are "German and racially valuable."

In October 1939, Freisler introduced the concept of 'precocious juvenile criminal' in the "Juvenile Felons Decree". This decree "provided the legal basis for imposing the death penalty and penitentiary terms on juveniles for the first time in German legal history". In the period 1933 through 1945, the courts sentenced at least 72 German juveniles to death, among them 16 year old Helmuth Hübener, found guilty of high treason for distributing anti-war leaflets in 1942.

The "Decree against National Parasites" (September 1939) introduced the term perpetrator type, which was used in combination with another Nazi term, parasite, The adoption of racial biological terminology portrayed juvenile criminality as parasitic, implying the need for harsher sentences. Freisler justified the new measures in the following manner: "In times of war, breach of loyalty and baseness cannot find any leniency and must be met with the full force of the law."

On 20 August 1942, Hitler promoted Otto Thierack to Reich Justice Minister, replacing the retiring Schlegelberger, and named Freisler to succeed Thierack as president of the People's Court. This court, set up outside the operations of the constitutional frame of law, had jurisdiction over a rather broad array of "political offences", which included crimes like black marketeering, work slowdowns, and defeatism. These crimes were viewed by Freisler's court as Wehrkraftzersetzung (the undermining of defensive capability) and were accordingly punished severely, the death penalty being meted out in numerous cases. It almost always sided with the prosecution, to the point that being hauled before it was virtually tantamount to a death sentence. Not surprisingly, it was viewed as a kangaroo court.

Freisler chaired the First Senate of the People's Court, and acted as judge, jury and prosecution embodied into one man. He also acted as court recorder; that way, he was responsible for the composition of the written grounds for the sentences that he wrote up in his own unique fashion, namely in accordance with his own notions of a "National Socialist criminal court".

The number of death sentences rose sharply under Freisler's stewardship. Approximately 90% of all proceedings ended with sentences of death or life imprisonment, the sentences frequently having been determined before the trial. Between 1942 and 1945, more than 5,000 death sentences were handed out, and of these, 2,600 through the court's First Senate, which Freisler headed. Thus, Freisler alone was responsible, in his three years on the court, for as many death sentences as all other senate sessions of the court together in the entire time the court existed, between 1934 and 1945.

Freisler was known for humiliating defendants and shouting loudly at them. He was known to be an admirer of Andrei Vyshinsky, the chief prosecutor of the Soviet purge trials, and reportedly copied his demeanor from Vyshinsky's. A number of the trials for defendants in the 20 July Plot before the People's Court were filmed and recorded. In the 1944 trial against Ulrich Wilhelm Graf Schwerin von Schwanenfeld, for example, Freisler shouted so loudly that the technicians who were filming the proceeding had major problems making the defendant's words audible. Graf von Schwerin, like many other defendants in the plot, was sentenced to death by hanging. Among this and other show trials, Freisler headed the 1943 proceedings against the members of the White Rose resistance group, and ordered many of its members to be executed by guillotine.

Freisler was conducting a Saturday session of the People's Court on 3 February 1945, when air raid sirens sounded as American bombers made a raid on Berlin. On that day, almost 1,000 Flying Fortresses dropped 3,000 tons of bombs on Berlin, in what was to be the heaviest air raid over Berlin ever. Government and Nazi Party buildings were hit, including the Reich Chancellery, the Gestapo headquarters, the Party Chancellery, and the People's Court.

According to one report, Freisler hastily adjourned court and had ordered that day's prisoners to be taken to a shelter, but paused to gather that day's files. Freisler was killed when an almost direct hit on the building caused him to be struck down by a beam in his own courtroom. His body was reportedly found crushed beneath a fallen masonry column, clutching the files that he had tried to retrieve, including those of Adjutant Fabian von Schlabrendorff, who was on trial that day and was facing execution for his role in the 1944 assassination plot against Hitler.

According to a different report, Freisler "was killed by a bomb fragment while trying to escape from his law court to the air raid shelter", and he "bled to death on the pavement outside the People's Court at Bellevuestrasse 15 in Berlin". Fabian von Schlabrendorff was "standing near his judge when the latter met his end".

Freisler's death prevented the sentencing and execution of von Schlabrendorff, who after the war became a judge of the Constitutional Court of the Federal Republic of Germany (Bundesverfassungsgericht).

Yet another version of Freisler's death states that he was killed by a British bomb that came through the ceiling of his courtroom as he was trying two women, who survived the explosion.

A foreign correspondent reported, "Apparently nobody regretted his death." Luise Jodl, the widow of General Alfred Jodl, recounted more than 25 years later that she had been working at the Luetzow Hospital when Freisler's body was brought in, and that a worker commented, "It is God's verdict." According to Mrs. Jodl, "Not one person said a word in reply."

Freisler is interred in the plot of his wife's family at the Waldfriedhof Dahlem cemetery in Berlin. His name is not shown on the gravestone.

Freisler is held up as a notorious and despicable abuser of judicial authority whereas his victims are honored for their role in attempting to uphold decency during a brutal and dictatorial regime. In Munich, several of his victims are honored:

• Sophie Scholl and her brother Hans Scholl are honored by the naming of the main square in front of the University, Geschwister - Scholl - Platz.
• Their friend Christoph Probst is honored by the naming of a street, Christoph - Probst - Strasse
• Their professor Kurt Huber is honored by the naming of another University square, Professor - Huber - Platz.

Freisler is the "fictional" character Judge Feisler in the 1947 Hans Fallada novel Every Man Dies Alone (Jeder stirbt für sich allein). In 1943 he tried and handed down death penalties to Otto and Elise Hampel, whose true story inspired Fallada's novel. Freisler has been portrayed by screen actors at least five times: by Rainer Steffen in the 1984 German television movie Wannseekonferenz, by Brian Cox in the British 1996 television movie Witness Against Hitler, by Owen Teale in the 2001 BBC / HBO film Conspiracy, by André Hennicke in the 2005 film Sophie Scholl – The Final Days, and by Helmut Stauss in the 2008 film Valkyrie.