The show, which stars Greg Kinnear as assassinated U.S. President John F. Kennedy and Holmes as his onscreen wife Jackie, hit headlines back in January (11) when The History Channel bosses scrapped it from their broadcast schedule, citing the programme as "not a fit for the History brand".
Subsequent reports suggested it was axed following pressure from surviving members of the clan, including Robert F. Kennedy, Jr., who branded the show "historically inaccurate".
However, chiefs at America's ReelzChannel snapped up the eight-part series and it debuted in America on Sunday (03Apr11).
Critics have been divided in their opinion of the show, but Fonda, who knew the Kennedy clan, is a big fan of the drama.
In a post on her blog, she writes, "I watched the first part of The Kennedys which I thought was pretty good.
"Kate does Jackie really well, I think. It's interesting. I knew the Kennedys and never knew that Jackie wanted a divorce before Jack ran for president. Didn't realise the extent to which father Joe ran the show. Talk about patriarchy! In that family it was quintessential!"