Just saw her in Cockneys and Zombies
Peter Hansen was the go-to guy whenever Science Fiction Theatre needed someone to play the professor or the doctor or whatever; his other pre-'58 TV work included a recurring role as Captain Farrell on Broken Arrow and a recurring role as Jim Bowie’s brother on, well, The Adventures of Jim Bowie.
Otherwise – well, in '54 you could see him in episodes of Schlitz Playhouse and an episode of The Loretta Young Show and an episode of Your Favorite Story and an episode of Public Defender and an episode of Cavalcade of America and an episode of Space Patrol and an episode of The Lone Ranger and an episode of The Lone Wolf.
(Was it, like, the Ranger’s wolf?)
Anyhow, he kept acting in the '50s and '60s and '70s and '80s and '90s and '00s, earning an Emmy for his soap-opera work and appearing in plenty of movies.
'30s Broadway actress turned WWII pin-up girl Marjorie Lord started getting TV work in the '40s – on Public Prosecutor and Your Show Time – and in the '50s appeared on some twenty different TV shows, including half-a-dozen Fireside Theatre episodes, before starting her long Make Room For Daddy run in '57.
David Hedison (who started his career as Al Hedison) was on television in 1955, although his most memorable appearances of the era were in the films “The Fly” and “The Enemy Below”.
Hadn’t thought about soap opera stars. Both Bill Hayes and Susan Seaforth Hayes got their starts in the early 50s and have recently been on Days of Our Lives.
Another early starter is Peggy McCay (Caroline Brady).
Ralph Waite (Father Matt) probably doesn’t qualify since his sole pre-58 appearance was a one-off host bit.
Rosemary Harris – Aunt May to Tobey Maguire’s Spider-Man – was in a few TV movies pre-1958, and got roles in a few episodes of Alfred Hitchcock Presents, and appeared on Studio One In Hollywood and The DuPont Show Of The Week – returning for more of that last one in '58, when they cast her in productions of “A Tale Of Two Cities” and “Wuthering Heights”. That was also the year she did yet another TV movie, playing the Grace Kelly part in Dial M For Murder.
Apparently she’s now filming yet another other TV movie, set to air later this year.
Four years earlier she insisted that her coronation be televised (over the objections her Prime Minister, Sir Winston Churchill.
Can we count Verne Gagne wrestling live on the DuMont Network in the '50s?
Shouldn’t that say he was arrested for speeding in Mayberry RFD?
added just in case.
Jamie Farr’s first TV credit was in 1957, although he has movie credits dating back to '55.
Micky Dolenz was 6 years old when he starred as Corky on Circus Boy.
Shirley Jones had her first TV gig when she was only 17, way back in 1950.
Angie Dickinson and Ellen Burstyn both racked up a bunch of credits in the early-mid 1950’s.
Rip Torn’s had a good long career, dating back to his work in '56 on Kraft Theatre and The United States Steel Hour and The Alcoa Hour – all of which he kept performing on in '57, the same year he did Alfred Hitchcock Presents and The Restless Gun and The Seven Lively Arts and The Kaiser Aluminum Hour; he’s been pretty busy since.
Robert Vaughn racked up well over a dozen pre-1958 TV credits – Playhouse 90, Gunsmoke, Medic, The Millionaire, West Point, and so on – before he became an Oscar-nominated actor with a fine big-screen role in 1959. And he’s still working.
Eerie you should have written that when you did. :eek: 
Robert Redford.
As far as I can tell, Redford’s TV debut is 1960, which is the wrong side of the OP’s line. By contrast, Robert Morse, who’s been so good on Mad Men as to earn four Emmy nominations for it, was on Matinee Theatre in '57, and The Alcoa Hour in '56, and Goodyear Playhouse in '55, and The Secret Storm in '54.
Marion “Mrs Cunningham” Ross was on The George Sanders Mystery Theater and Matinee Theatre in 1957, and Ford Star Jubilee and The Millionaire in 1956, and Front Row Center in 1955, and The Loretta Young Show and The Lone Ranger in 1954, and Life With Father and Cavalcade of America back in 1953.
Julie Andrews performed in what many consider to be the first made-for-TV movie, High Tor in 1956.
Vin Scully has been broadcasting Dodger baseball games since 1950.
Micky was born in 1945, and “Circus Boy” debuted in 1956, so he was 11 years old.
Sheila James, who is best remembered as Zelda Gilroy, the harmless stalker of Dobie in *The Many Lives of Dobie Gillis, * was also a regular on two 1950’s comedies, The Stu Erwin Show and The Bob Cummings Show.
She’s really led a remarkable life. After her TV roles dried up, she graduated near the top of here class at Harvard Law School. After returning to California, she became the first openly-gay member of the California Assembly and also winning a seat in the State Senate.
She’s still active in Cali politics at the age of 74.