He served in the Legislative Assembly of Manitoba from 1907 to 1922, and was a prominent cabinet minister in the government of Tobias Norris.

He was educated in Winnipeg public schools, and received a Bachelor of Arts degree from Gustavus Adolphus College.

Manitoba was governed by Rodmond Roblin's Conservatives during this period, and Johnson served as a member of the opposition.

In 1915, the Roblin government was forced to resign from office following a corruption scandal involving the tendering of contracts for new legislative buildings.

Many members of Norris's government favoured a negotiated settlement with the strikers, and the subsequent legal charges against the strike leaders were launched as a private prosecution by the Citizens' Committee of one Thousand, funded by the federal Department of Justice, and allowed to proceed by Johnson as Attorney General.

Later, Johnson defended the prosecutions in the spring of 1921 when Fred Dixon brought a motion to the floor of the Manitoba legislature seeking the release of the imprisoned strike leaders.