Leah Remini's deal to join "The Real Housewives of Beverly Hills" nearly collapsed before it was finalized ... with negotiations going down to the wire ... TMZ has learned.

Production sources tell TMZ ... Leah was in the final stages of talks to become a full-time Housewife for the upcoming season when the deal hit some turbulence a couple of weeks ago.

We're told producers became concerned the two sides might not get it done ... but Leah ultimately signed on at the 11th hour, locking in her spot alongside the other women.

The rest of the cast has already been filming for the past couple weeks ... so Leah will be jumping into the mix after the season is already underway.

As we reported, Leah is making a major move into the Bravo universe as a full-time Housewife for Season 16.

It's a big get for the franchise ... Leah's one of the most recognizable TV stars to ever join the Housewives world, thanks in large part to her longtime run as Carrie Heffernan on "The King of Queens."

And if her history is any indication, Leah won't be shy about speaking her mind once the cameras start rolling.