Luc Letellier de Saint-Just, (May 12, 1820 – January 28, 1881) was a Canadian politician. He also served as the third Lieutenant Governor of Quebec (1876–1879).
A notary by training, Letellier belonged to an old and prominent family. He was a half-brother of Horace Bélanger. In 1851, he was elected in a by-election to the Legislative Assembly of the Province of Canada as a supporter of Louis-Hippolyte Lafontaine. He was defeated in a general election a few months later by his rival Jean-Charles Chapais. In 1860, Letellier won election to the legislative council of the united province and, in 1863, he was appointed minister of agriculture in the Reform - rouge Cabinet of Joint Premiers John Sandfield Macdonald and Antoine-Aimé Dorion. The government fell the next year, however, in favour of a Tory – Parti bleu administration.
Letellier opposed Canadian Confederation prior to 1867, but accepted it once it became a reality. He was appointed by royal charter as a charter member of the Canadian Senate when it was created in 1867. He sat as a "Nationalist Liberal", and was Leader of the Opposition in the Senate from 1867 until the 1872 election when the Liberals took power under Alexander Mackenzie. Letellier became Leader of the Government in the Senate and Minister of Agriculture in Mackenzie's Cabinet. He had also attempted to concurrently win a seat in the Quebec legislative assembly, but was defeated in his attempts in 1869 and 1871 to win election.
In 1876, Mackenzie advised the Governor General of Canada to appoint Letellier to the position of lieutenant-governor of Quebec. As lieutenant governor, he dismissed the government of Conservative Quebec Premier Charles-Eugène Boucher de Boucherville on March 1, 1878, despite the fact that the government enjoyed a 20-seat majority in the Quebec legislative assembly and a two-to-one majority in the legislative council. Letellier justified the dismissal on charges that the government was acting incompotently and corruptly on the matter of railway legislation. He also argued that if the de Boucherville government hadn't made concessions to "rings" of interest within the legislature on the issue, it would lose the legislature's support. De Boucherville called the move a "coup d'etat", and complained to the Governor General of Canada. Both houses of the Quebec legislature passed motions of censure against the lieutenant-governor.
When the federal Conservatives under Sir John A. Macdonald defeated the federal Liberals in the 1878 election, the new federal Cabinet tried to have Letellier dismissed as lieutenant-governor of Quebec. The Governor General, the Marquess of Lorne, referred the matter to the Colonial Secretary in London who advised him to follow the advice of his ministers. Letellier was dismissed.