In 1948 Columbia Pictures producer Jules White teamed Quillan with veteran movie comic Wally Vernon for a series of comedy short subjects.

White emphasized extreme physical comedy in these films, and Vernon and Quillan made a good team, enthusiastically engaging in pratfalling, kick-in-the-pants slapstick.

He was a regular on the Anthony Franciosa sitcom Valentine's Day from 1964 to 1965, and from 1968 through 1971 he appeared as Eddie Edson on the comedy Julia opposite actress Diahann Carroll.

One notable appearance of the era was his role of Sandy in the 1954 Vincente Minnelli directed musical Brigadoon, starring Gene Kelly, Van Johnson and Cyd Charisse.

Quillan also appeared in the uncredited role of Mr. Cassidy in the 1969 Gene Kelly film adaptation of Hello, Dolly!, starring Barbra Streisand and Walter Matthau and featuring Louis Armstrong.

After meeting and befriending actor and director Michael Landon, he played numerous bit roles in the popular television series Little House on the Prairie.