His first teleplay was performed on "Chevrolet Tele-Theater" in 1949. During the early 1950s, he became a leading scripter for live television dramas, contributing six teleplays to "Goodyear Television Playhouse" (in 1953-1954), two to "Medallion Theatre" (1953–1954) and four to "Playhouse 90" (1957–1959). He also wrote for "The Philco Television Playhouse" (1954), "Producers' Showcase" and "Studio One". After Eileen Heckart appeared in "The Haven" (on "Philco Television Playhouse"), his 1953 play about a troubled marriage, Mosel and Heckart became friends, and he wrote several scripts especially for her, including the 1953 "Other People's Houses" (on "Goodyear Television Playhouse") about a housekeeper caring for her senile father.