I don't think so, not in my recollection. I have seen regular characters move from one existing series to being regulars on another existing series but that tends to happen more often with supporting-ish characters.
After Stargate SG-1 ended, Samantha Carter became the new leader of the Atlantis expedition in the 4th season of Stargate Atlantis.
A couple years after Star Trek: The Next Generation ended, Worf became the new Strategic Operations Officer during the 4th season of Star Trek: Deep Space 9.
After Buffy the Vampire Slayer ended, Spike became a regular during the 5th season of Angel.
Connie Rubirosa was the ADA during the final 4 seasons of Law & Order. She then became the new ADA on Law & Order: Los Angeles when they retooled the show midway through the 1st season.
Then there's John Munch, who had been a regular on Homicide: Life on the Street. After that show ended, they made a snap decision to make him a regular on Law & Order: Special Victims Unit. He was there from the beginning but I believe he was a fairly last-minute addition to the pilot.
I suppose I can recall a few series leads going on to become leads on other shows.
Alan Shore from The Practice to Boston Legal.
Mike Logan had been one of the 2 main detectives on Law & Order during its first 5 seasons. Then, about a decade after he left, he became one of the co-leads on Law & Order: Criminal Intent during Seasons 5-7.
Lennie Briscoe had been one of the main detectives on Law & Order during Seasons 3-14. When he left, he had a major supporting role on the short-lived spin-off Law & Order: Trial by Jury. Sadly, he only appeared in the first 2 episodes before the actor died of cancer. (Also, Arthur Branch served double duty that year as a regular on both Law & Order and Law & Order: Trial by Jury.)
Sarah Jane Smith was a sort of co-lead on the original Doctor Who during Seasons 11-14. About 3 decades after she left, the BBC gave her a spin-off series, The Sarah Jane Adventures. (They had also attempted an earlier spin-off with her in the early 1980s called K-9 & Company, pairing her up with the Doctor's robot dog companion from the late 1970s.)
Then you've got series regulars that jumped from one series to another & back again.
IIRC, one of the daughters from The Cosby Show left to go to college, launching the spin-off A Different World. While A Different World continued for 6 seasons, the Cosby daughter left Hillman College after only 2 seasons and ended up back on The Cosby Show.
Alexandra Cabot was the ADA for several seasons on Law & Order: SVU. In Season 5, she went into the witness protection program. A couple years later, she came out of witness protection and was the new bureau chief on the short-lived Conviction spin-off. After Conviction was canceled, she came back semi-regularly on Law & Order: SVU during Seasons 10-13.