He qualified to practice as a provincial land surveyor in Quebec in 1878 and as a dominion land surveyor for Canada in 1881; he also later qualified as a surveyor for Ontario and Manitoba.
He later became chief engineer for the Montreal and Pacific Junction Railway, also serving as a director for the company.
Casgrain was also chief engineer for the Montreal Turnpike Trust.
He was president of the Montreal Herald.
In 1885, he married Ella, the daughter of lumber merchant James William Cook.
They lived at 'Bijou', their home in the Golden Square Mile of Montreal.
He died in office in 1939.