Before '58, Betsy Palmer acted in half-a-dozen episodes of Goodyear Playhouse and half-a-dozen episodes of Studio One In Hollywood and made the rounds on episodes of The United States Steel Hour and episodes of To Tell The Truth and episodes of Climax! and episodes of Kraft Theatre and episodes of Armstrong Circle Theatre and episodes of Lux Video Theatre and et cetera, dating back to her television debut on Martinsville, USA back in 1951 before hosting Wheel of Fortune in 1952.
No, the other Wheel of Fortune.
You maybe remember her as the mom of Jason Voorhees, in Friday the 13th.
Jimmy Lydon is still around. Although best known today as a television producer, he began acting in the 1930s as a child actor in Hollywood. By 1950, he gained his first starring television role in CBS’ first soap opera The First Hundred Years which ran for 300 episodes and ended in 1952.
Nancy Malone is also still alive. She co-starred in The First Hundred Years with Lydon, but she also has starred in a range of other television projects from the late 1940s until 1985.
Gerrianne Raphael was an occasional guest star with Malone and Lydon in The First Hundred Years. She later performed a wide range of roles, including television voice work like the original Thundercats animated series and acting roles such L&O:SVU in 2008.
Jeffrey Silver is still with us. A child actor, he is best known at the last surviving member of the ***Blondie ***radio program, based upon the popular comic strip and as part of the cast of the Bob Cummings Show. His first television role was in an episode of 1950s The Silver Theatre..
Douglas Dick, an actor and a writer was born in 1920. He co-starred in numerous productions from Alfred Hitchcock’s Rope to the first filming of the literary classic The Red Badge of Courage. His first television role was in 1951’s Fireside Theatre.
Peter Marshall is 88 years young today. He has some credits in the early 50s and one, for a TV pilot, from 1949. Apparently still working on radio.
I pick Jo Anne Worley to block. Which leads to Laugh In folk. She doesn’t qualify but Arte Johnson does. Only one credit in quite some time and that was voice work in 2005.
Not '49, but in '59, Earl Holliman starred in the pilot episode of The Twilight Zone as the monologuing amnesiac wandering a deserted town’s empty streets, which (a) I’m guessing most folks would count as a golden-age-of-TV milestone but (b) runs afoul of the OP’s dividing line – so I’ll add that Holliman made his television debut in '57, acting on Matinee Theatre and Playhouse 90 after winning the Golden Globe for his work in the movies, after serving in the Navy during WWII.
It’s not surprising that Connie Sawyer got lots of pre-'58 work – on The Arrow Show in '48, and on The Milton Berle Show in '49, and on The Colgate Comedy Hour in '50, and so on for Armstrong Circle Theatre and The Jackie Gleason Show and et cetera.
It’s a little surprising, though, that after six decades of solid work she turned one hundred and then acted on Two Broke Girls and NCIS: Los Angeles and Ray Donovan and New Girl. (She’s also in a movie set to come out later this year.)
Marian Collier made her TV debut on The George Burns and Gracie Allen Show in '57. That was apparently her only pre-'58 TV appearance, but…
Naw, that’s weak; call it April Fools’. Let’s go with Barry Gordon, who got tons of acting work after – er, one pre-'58 TV credit, on The Jack Benny Program. Sonofabitch.
Okay, how about Van “The Green Hornet” Williams, who – really? Just the one TV movie, back in '54? Dangit.
Fine. Whatever. I’m going deep. Aki Aleong: still acting as of this year, and with THREE whole pre-'58 television credits. Yeah. Robert Montgomery Presents, plus Producers’ Showcase, and also The Californians. Woo!
Anne Jackson married Eli Wallach in '48, and started acting on television in '49, and has pretty much kept on keeping on with the marriage and the acting since.
So in 1957, you could see her on episodes of Studio One In Hollywood with Margaret Hamilton and Eddie Bracken; in 1956, General Electric Theater with Ronald Reagan and Roddy McDowall; in 1955 she got work on Goodyear Playhouse, since she’d spent 1954 and 1953 doing the same on The Philco-Goodyear Television Playhouse; and so on for Armstrong Circle Theatre and Academy Theatre and Lux Video Theatre and Kraft Theatre and so forth; and also appearing in yet other television productions, with everyone from James Dean to Leslie Nielsen, back when.
Comic-book character Peter Wyngarde acted in a made-for-television version of Rope back in 1950, and starred in a Tale Of Two Cities miniseries in 1957, and did a number of TV movies in between, and got work on half-a-dozen TV shows before '58.
(He’d have more golden-age-of-television credits, but pre-'58 he was also busy on stage with Alec Guinness, and on the big screen with Richard Burton, and et cetera. Anyhow, now in his eighties, he’s slowed down but is still working – having most recently narrated a documentary earlier this year.)
Before his Emmy-nominated role as Cliff Huxtable’s dad, Earle Hyman was getting television work as far back as '54 (in Look Up And Live) and '55 (as the title character in a made-for-TV version of Othello); in '57, you could see him as a small-screen Jim in The Adventures of Huckleberry Finn – but before that, you could see him in a TV movie of The Green Pastures with Terry Carter.
Because, see, back before Carter was the original Colonel Tigh – or racking up an Emmy nomination of his own – he was a regular on The Phil Silvers Show from '55 to '59. But that didn’t stop him from appearing, in '57, on The Big Story with a young Louis Gossett Jr making his screen debut long before winning himself an Oscar and some Emmys and a couple of Golden Globes.
New England playwright Warren Frost served in WWII before spending three years as stage manager on the Philco Television Playhouse, after which he fielded a couple of small-screen roles in '57 – and then kept acting, on and off, for the next forty years: from Perry Mason to Matlock, from Playhouse 90 to Twin Peaks, and et cetera.
(You maybe remember him from Seinfeld, as Susan’s disapproving patrician father, who loved John Cheever deeply, in a way you could never understand?)
Mark Rydell made his television debut in '53, as a young actor working alongside James Dean on Omnibus; almost fifty years later, he was directing the James Dean TV movie that got him (and James Franco) an Emmy nomination.
Anyhow, in 1954 you could see Rydell working with Hume Cronyn and Jessica Tandy on The Marriage; in 1955, with John Cassavetes and Robert Preston on The Elgin Hour; and in 1956, he apparently became a castmember on both As The World Turns and The Edge of Night – which didn’t stop him from popping in for an episode of Navy Log in 1957.
Brett Halsey made his TV debut on Waterfront with Charles Bronson in '54 before bouncing around from Dr. Hudson’s Secret Journal to Brave Eagle to Gunsmoke to Tales of the 77th Bengal Lancers to The 20th Century-Fox Hour before '57 – when you could see him in his recurring role on West Point alongside young up-and-comers Leonard Nimoy and Larry Hagman.
('57 was also the same year he made the rounds on Highway Patrol and Matinee Theatre, as it happens – and he was still appearing on the big screen as of this past June, the same month he turned eighty.)
Marvin Kaplan, who made his big-screen debut way back in '49 with Tracy and Hepburn in Adam’s Rib, made his small-screen debut a year later and soon had a steady gig on Meet Millie from '52 to '55, during which time he also (a) got acting work on General Electric Theater and The Ford Television Theatre and et cetera, and (b) appeared on Stars In The Eye with the likes of Jack Benny and George Burns and everyone else from Lucille Ball to Art Linkletter.
He was also on The Red Skelton Hour, both before and after the OP’s cut-off date. And in the '60s, he had a recurring role on The Mod Squad; in the '70s, a recurring role on The Chicago Teddy Bears; in the '80s, a recurring role on Alice; in the '90s, a recurring role on On The Air; and in the '00s, a recurring role on Becker – after which he (a) turned eighty, and (b) promptly picked up his first ‘producing’ credit, easy as writing the movie’s screenplay.
He was also the voice of Choo-Choo on Top Cat and, along with Arnold Stang (the voice of TC himself), was co-owner of the service station Jonathan Winters trashed in It’s a Mad, Mad, Mad, Mad World.
Yvonne White got plenty of pre-'58 TV work – on The Adventures of Superman and Dragnet and Bachelor Father and Highway Patrol and Navy Log and Studio 57 – and in '59 appeared on General Electric Theater with Bart Braverman, who’d spent the golden age of television acting on The Star And The Story with Angela Lansbury, and Warner Brothers Presents with Elizabeth Montgomery, and so on for State Trooper and Telephone Time and et cetera.
(Oh, and he was Giuseppe in the ‘Italy’ episode of I Love Lucy.)