MacLennan taught at local district schools to earn money for his medical studies.

His extended family over the years now resides in Tyne Valley, Prince Edward Island and Mainland Nova Scotia.

During his time as an MP, he was instrumental in bringing the railway to the west side of Cape Breton Island, thereby spurring the growth of Inverness as a coal-exporting boom town in the first quarter of the 20th century.

MacLennan represented Inverness (as a Conservative) for one term in the Nova Scotia legislature (1882-1886).

He died of a stroke on August 27, 1908, in Chéticamp, Cape Breton, while campaigning for a fourth term in the 1908 federal election.