He later worked as a
purser on
steamships that travelled between Montreal and
Kingston. In 1850, he was promoted to freight agent, at first based in
Kingston and later in Montreal. In 1853, with his brother, he founded a grain and shipping company, later known as the Montreal Transportation Company with McLennan as president. in his studio in Montreal in 1867. He served as a director for various
companies, including
Bank of Montreal, Canada Paper Company, the British America Fire and Life Assurance Company and
Sun Life. McLennan was also president of the International Coal Company Ltd and the
Black Diamond Steamship Company. From 1872 to 1874, he was president of the Montreal Board of Trade; he also represented the Board of Trade on the Montreal Harbour Commission. McLennan served on the board of governors of
McGill University and was president of the
St. Andrew's Society of Montreal from 1885 to 1886. He retired from business in 1898. == Personal life ==