He was a son of United Empire Loyalist Major Nicholas Hagerman (1761–1819) J.P., and his wife Anne (1758–1847), daughter of John and Mary (Campbell) Fisher, formerly of Killin.
Kit's grandfather, Christopher Hagerman (b.1722), was a Dutch officer in the service of the Prussian Army who had fought for George II of Great Britain at the Battle of Culloden, 1746.
north of Albany, in 1783, on completion of the war, Nicholas Hagerman signed with Captain Alexander White's company of Associated Loyalists.
Hagerman began his legal career in the Kingston, Ontario law offices of his father, one of the first appointed barristers in Upper Canada.
[1] He served in his father's militia regiment during the War of 1812, becoming the aide-de-camp to Lieutenant-General Gordon Drummond, who regarded him highly; Hagerman later gained the rank of lieutenant-colonel.
By this time, Hagerman was one of the most prominent people in Upper Canada, and came into contact with young fellow Kingstonian lawyer John A. Macdonald, also a Conservative, who was then just beginning his own political career.
Young Kingstonian Oliver Mowat, who had apprenticed as a lawyer with Macdonald, was at that time beginning a career which would see him become an Ontario Liberal Party premier for a record 24 years (1872–96).
In England in 1834, he married Elizabeth Emily, daughter of the British Deputy Secretary at War, William Merry (1762–1855) of Lansdowne Terrace, Cheltenham, by his wife Anne, daughter of Kender Mason of Beel House, Buckinghamshire, the sister of Henry Mason, who married a niece of Horatio Nelson, 1st Viscount Nelson.