[1] His father, Milton, sold insurance and his mother, Katherine Louise (née Ostertag), was a housewife.

[5][6] Hickman's first screen appearances were as an extra in The Grapes of Wrath (1940) and Men of Boys Town (1941), in which his brother Darryl was featured.

Other early screen appearances were in the 1942 Our Gang comedy Melodies Old and New, Captain Eddie (1945), The Hoodlum Saint (1946), and Faithful in My Fashion (1946).

In 1946, Hickman played young Chase in the movie The Secret Heart which starred Claudette Colbert, Walter Pidgeon, Lionel Barrymore, and June Allyson.

[7][8] Heaven Only Knows (1947), in which he appeared, starred Bob Cummings, who would play a major role in Hickman's career.

Hickman also appeared in Her Husband's Affairs (1948), The Boy with Green Hair (1948), The Sun Comes Up (1949), Mighty Joe Young (1949), and The Happy Years (1950), which starred Darryl.

[9] Hickman focused on his studies for a few more years, then returned to acting with appearances in Public Defender, The Loretta Young Show, Lux Video Theatre, and Waterfront.

He played Dobie for four years (with fellow former Loyola student Bob Denver as his sidekick Maynard G. Krebs).

He and Annette Funicello appeared together in an episode of the drama The Greatest Show on Earth, starring Jack Palance.

He guest-starred on Vacation Playhouse; Ironside; Insight; The Flying Nun; My Friend Tony; Walt Disney's Wonderful World of Color ("My Dog, the Thief"); Mod Squad; Love, American Style; Karen; Kolchak: The Night Stalker; Perry Mason; and Ellery Queen.

He reprised his most famous role in Whatever Happened to Dobie Gillis?, a one-shot pilot, and appeared in the TV movie Don't Push, I'll Charge When I'm Ready (1977).

He could be seen in Surviving Gilligan's Island: The Incredibly True Story of the Longest Three Hour Tour in History and Angels with Angles (2005).