Ashida was born in Fukuchiyama, Kyoto, and studied French civil law at Tokyo Imperial University. After graduation, he worked in the Ministry of Foreign Affairs for twenty years.

In 1932, Ashida ran his first successful campaign for a seat in the House of Representatives as a member of the Seiyukai Party. He sided with Ichirō Hatoyama's "orthodox" wing following the Seiyukai's split in 1939.

After the war, Ashida won a seat in the new Diet as a member of the Liberal Party, which soon merged with Kijūrō Shidehara's Progressive Party to form the Japan Democratic Party. Ashida was elected president of the new party, and became Minister of Foreign Affairs in 1947 under Socialist prime minister Tetsu Katayama.

Ashida became prime minister in 1948, leading a coalition government of Democratic and Socialist members. His tenure ended just seven months after it began. Two of his cabinet ministers were accused of corruption in the Showa Electric scandal, which forced the cabinet to resign.

Ten years later, in 1958, Ashida was cleared of all charges in relation to the incident. He died a year later at the age of seventy-one.