Duggan developed a friendship with Broadway director Daniel Mann[2] on a troop ship when returning from the war.

Duggan appeared on Broadway[3] in The Rose Tattoo, Gently Does It, Anniversary Waltz, Fragile Fox, and The Third Best Sport.

Among his roles were playing a pastor and padre, sheriff and warden, doctor and professor, numerous judges and generals, and three times the President of the United States.

Duggan did voice-over work including Ziebart's 1985 Clio Award-winning "Friend of the Family (Rust in Peace)" television commercial.

[4] In 1957, Duggan appeared as Major Ellwood in the TV Western Cheyenne in the episode titled "Land Beyond the Law".

In the opening episode, "The Peacemaker" or "Judgment Day", Duggan plays Jim Rexford; Brown is cast as Dave, and Steele as Sergeant Granger.

In 1959, Duggan was contracted to Warner Brothers Television where he was cast in ABC's Bourbon Street Beat,[5] in which he portrayed Cal Calhoun, the head of a New Orleans detective agency.

He appeared as an incorrigible criminal trying to gain amnesty in the 1962 episode "Sunday" of the ABC/WB series, Lawman, starring John Russell.

He had a recurring role as General Ed Britt in the second and third seasons of the ABC war series, Twelve O'Clock High.

Even earlier, Henry Fonda had played essentially the same role in the movie based on Earl Hamner's writing that inspired them both, Spencer's Mountain (1963), although the character's name was different.