Lareau was admitted to the Quebec bar in 1870 and set up practice in Montreal.
He was granted a Bachelor of Civil Law by McGill College in 1874.
Lareau became a professor of law at the college.
He was named Queen's Counsel in 1879.
In 1880, he married Marguerite Robillard.
He was an unsuccessful candidate for a seat in the House of Commons in 1882.
Lareau contributed to the journals La Patrie and Le Temps and was coeditor of the Lower Canada Jurist with John Sprott Archibald.