The Premier League club confirmed on their website that he had signed a one-year deal.
The former Arsenal skipper, 33 last Tuesday, became only the 14th player to move from Arsenal to Spurs in almost a century and will earn a unique place in the record books as the first to appear in competitive action for London's three biggest clubs.
Tottenham manager Harry Redknapp was not worried about the reaction of the fans and insisted Gallas's decision to join Spurs said much about the player's character.
"It's not like I've signed the Yorkshire Ripper," he told reporters referring to English serial killer Peter Sutcliffe. "He (Gallas) is a footballer. When he leaves here he might go and play for West Ham, who knows?
"He will come here with a point to prove ... if he had wanted an easy life he would have taken some big money in Greece or somewhere. He has put himself under real pressure by coming here and you have to give the man some credit.
"It's not like he came here for a big pay day. I promise you, he came because he wanted to play and he's taken the hardest challenge of all to come to Tottenham."
Moves between the clubs are rare and Gallas is only the fourth player to join Spurs having been at Arsenal in the last decade after Rohan Ricketts, Jamie O'Hara and David Bentley.
"I think he (Gallas) is a great player on a free transfer," Redknapp said. "I've signed a good player to keep Tottenham going forward instead of backwards."
Gallas is a peerless reader of the game who also scores goals and there has far more in his armoury than the petulant display most neutrals remember when he sat on the pitch after Arsenal's 2-2 draw at Birmingham City in February 2008.
