In 1829, he secured a position in the office of John Beverley Robinson and then partnered with Solicitor General Christopher Alexander Hagerman.

By 1839, he had broken with his Family Compact friends and set his political goal: "To found a party on a larger basis than ever had been formed before."

Although his first attempts to establish a conservative alliance with French Canadians failed, Draper played an important role in enabling Louis-Hippolyte Lafontaine to take office in 1842, even at the cost of resigning himself and of seeing Robert Baldwin succeed him as attorney general for Canada West.

At the next election, in 1844, the supporters of Draper, Viger and Governor Charles Metcalfe, including the young John A. Macdonald, won a majority.

In 1847, with the arrival of Lord Elgin, Draper resigned from the position of attorney general and became a judge of the Court of Queen's Bench.