Matthew Leonard was born in Philadelphia, Pennsylvania on 20 July 1886. 

He was the son of Irish Roman Catholic parents, John Leonard, a shoemaker, and Sarah Barry (b. 1853). His father's exact Irish origins are not clear but his mother have hailed from Toome, a village in northwest Co Antrim and was the daughter of Luke Barry and Bridget Magee. 

When Leonard's parents migrated to the USA is not certain.

Matthew and his mother returned to Ireland sometime prior to 1890 and settled in Brecart near Ballymena in Co Antrim; Matthew's only sibling, his sister Mary, was born there on 1 April 1890. At the time his father was indicated to still be residing in America and if he ever returned to Ireland is not known. His mother was listed as a widow on the 1901 census when the family were living at 8 Brecart, Toome, Co Antrim, the home of his maternal grandmother Bridget Barry, a farmer. After leaving school Matthew worked for a grocers and he and his family had relocated to Belfast by the time of the 1911 census and show up living at 23 Chatsworth Street, Pottinger, east Belfast, Co Down. Matthew was described as a grocer's assistant and his sister Mary as a machinist. He later went to work for a jewellers, Joseph Rea's in Ann Street, Belfast City Centre which is still in operation today. He later left to go to sea before Easter 1912.

Matthew was on the Titanic for her delivery trip from Belfast to Southampton. When he signed on again in Southampton on 4 April 1912 he gave his address as 45 Chatsworth Street, Belfast. As a third class steward he could expect monthly wages of £3, 15s. The Titanic was his first working sea voyage. 

Matthew Leonard died in the sinking and his body, if recovered, was never identified.

Sarah Leonard made an application for arbitration and appointment in respect of Malcolm (sic) Leonard, the son of the applicant. Deceased was drowned in the Titanic disaster. Belfast News-Letter, 4 November 1912

In following years his mother was to face calamity herself when she fell from a moving tram:

An old woman of sixty years named Sarah Lennard (sic), residing at Chatsworth Street, fell from a tram yesterday and sustained injuries, for which she had to be treated in the Mater Hospital. Northern Whig, 7 December 1918

What became of Matthew's mother and sister in later years remains unknown.