Timlin then became a Trial Attorney at the Criminal Division of the United States Department of Justice from 1961 to 1964.

[1] From 1964 to 1966, Timlin served as Assistant United States Attorney of the Central District of California.

On leaving that role, he was in private practice for one year until he became the City Attorney of Corona, California, a position he held from 1967 to 1970.

He was then appointed as an Associate Justice of the 4th District Court of Appeal in California by Governor George Deukmejian, a role he served in from 1990 to 1994.

[1][2] Timlin was nominated by President of the United States Bill Clinton on April 26, 1994, to a new seat created by 104 Stat.