His mother took her sons to acting classes every day after school; he eventually studied dance, drama, diction, dialects, martial arts, and equestrian riding.

[2] He had his first speaking part at age 9, a small role in the film So Big starring Jane Wyman and Sterling Hayden.

[2] He continued to appear in small roles in feature films such as Good Morning Miss Dove, and Everything But the Truth, and made numerous guest-starring appearances on television series, including Lassie, The Adventures of Ozzie and Harriet, Wagon Train, Fury, Circus Boy, and The Loretta Young Show.

In 1959, Osmond played 16-year-old "Tommy" in the episode "Dead Aim" of the ABC/Warner Brothers western series Colt .45, starring Wayde Preston.

John Doucette was cast as the bounty hunter Lou Gore, and Bing Russell portrayed Jed Coy in the episode.

[7] After Leave It to Beaver ended in 1963, Osmond continued to make occasional appearances on such television series as CBS's Petticoat Junction, The Munsters, and a final return appearance on Lassie in the episode "A Matter of Seconds" (1967) as a motorcycle delivery man who offers the hitchhiking collie a lift in his sidecar.

"[2] In 1970, Osmond joined the Los Angeles Police Department (LAPD) and grew a mustache in an effort to remain relatively anonymous among citizens, although not his co-workers.

[17] In 1983, Osmond appeared as a game show participant and celebrity guest star on the Match Game-Hollywood Squares Hour, along with Beaver co-stars Jerry Mathers, Richard Deacon and Jeri Weil.

Osmond returned to acting in 1983 reprising his role as Eddie Haskell in the CBS made-for-television movie Still the Beaver, which followed the adult Cleaver boys, their friends, and their families.

[2][21] In 1987, Osmond was honored by the Young Artist Foundation with its Former Child Star "Lifetime Achievement" Award for his role as Eddie Haskell.

[2][4][21] Following his retirement from the police force, Osmond handled rental properties in Los Angeles County and made occasional personal appearances at film festivals, collectors' shows, and nostalgia conventions.

[30] Osmond was the co-author, along with Christopher J. Lynch, of the book Eddie: The Life and Times of America's Preeminent Bad Boy, which was published in September 2014.

[36] Osmond testified at his disability hearing in 1986 that in 1971 he was called into LAPD Internal Affairs and asked to disrobe to prove he was not John Holmes.

Osmond claimed that the film's advertising defamed him, but the trial court dismissed the case and Osmond appealed to the California Court of Appeals, which also ruled against him, stating that there was no evidence that the owner of the bookstore was aware of the defamatory language on the packaging and therefore had not acted with "malice" in selling the video.