Hagerman began his legal career in the
Kingston, Ontario law offices of his father, one of the first appointed
barristers in
Upper Canada. 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. Hagerman kept a journal of his war experiences, and this has survived; it is kept in the reserved collection of the City of Toronto Library. Hagerman was
called to the bar in 1815. He was called to the Bar of Upper Canada in 1815, and became a
King's Counsel that same year. In 1829 he was appointed solicitor general for the province, and in 1837 he became attorney general. He was the first Canadian-born attorney general of Upper Canada. As such, he had to deal with the
Upper Canada Rebellion in late 1837, which unsuccessfully attempted to overthrown the dominance of the
Family Compact. Hagerman was a leading member and advocate of the
Family Compact, a staunch conservative, and well known for his loyalty to the
Church of England. He was appointed judge for the Court of Queen's Bench in 1841. 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. With Hagerman becoming a judge and thus vacating his parliamentary seat, Macdonald won election for Kingston in 1844 into the Province of Canada parliament, and later became Canada's first prime minister in 1867. 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). ==Personality==