Educated at McGill University, Montreal, Abbott became a lawyer in 1847 and was made queen's counsel in 1862. He served as dean of the McGill faculty of law from 1855 to 1880. He was elected to the Legislative Assembly of the then-united province of Canada in 1857 and continued to represent his native county, Argenteuil, until 1887, except during 1874–80. In 1862 he served briefly as solicitor general in the government of John Sandfield Macdonald (Macdonald, John Sandfield) and Louis Sicotte before going over to the Conservatives after confederation in 1867.

As legal adviser to the shipping magnate Sir Hugh Allan (Allan, Sir Hugh), Abbott was implicated in the Pacific Scandal of 1873, in which Prime Minister John A. Macdonald (Macdonald, Sir John) was accused of awarding a railway construction contract to Allan in return for campaign funds. Abbott accordingly was defeated in the 1874 election and was not reelected to the House of Commons until 1880. Seven years later he was appointed to the Senate, in which he was made government leader. On the death of Macdonald in June 1891, Abbott emerged as compromise choice for prime minister, but he resigned the following year because of ill health. He was knighted in 1892.