In April 1918 he traveled to Florida to serve as an instructor at Camp Joseph E. Johnston where he was promoted to second lieutenant.

Arriving back in Oregon he began a correspondence with Franklin Delano Roosevelt that would last four years.

When George Luis Baker chose not to try for re-election as mayor, Joseph decided to run.

One of his first acts was to appoint his former coastal artillery colonel Berton K. Lawson as police chief of Portland.

A waterfront strike of longshoremen in 1934 was considered by Carson to be the most unpleasant event of his mayoral administration.

Carson married his first wife, Hazel Irene Jenkins of Pendleton, Oregon on March 26, 1926.

They had one daughter, Mrs. Richard (Joan) Staley, and one son, Lucian Joseph (August 10, 1939 – January 19, 1990).

He had a great interest in biography (his favorite work was The Life of John Marshall by Albert J. Beveridge), and portraits of the presidents were hung in his law offices.

Carson died of a coronary thrombosis suffered at his home on the morning of December 20, 1956.