Speed seals Bolton deal
Speed has penned a two-year deal at The Reebok Stadium after agreeing personal terms and passing a medical.
Fulham and Leeds had been linked with Speed, but Bolton won the race for his signature as Sam Allardyce continues his building plans for next season.
"I am delighted to sign a player of Gary's quality," said Allardyce.
"He's a very experienced Premiership player and will add much needed depth to our squad."
The 34-year-old has a wealth of experience as he holds the record for the most Premiership appearances.
Speed becomes the fourth new signing at Bolton this summer following the arrivals of Michael Bridges, Les Ferdinand and Radhi Jaidi.
The former Everton and Leeds man becomes the second player to leave Newcastle in the last 24 hours, with Hugo Viana having agreed a deal to return to former club Sporting.