Mendes completed a medical and agreed terms on Friday
Rangers have confirmed the signing of Portsmouth midfielder Pedro Mendes on a three-year deal.
The English Premier League club had accepted an offer of £3m for the 29-year-old Portuguese.
Mendes travelled to Glasgow on Friday to discuss personal terms and complete a medical with the Ibrox club.
He said: "It's such a great club and there is the chance to fight for the championship and win cups. You can't expect anything but to win things."
Mendes immediately threw down the gauntlet to Celtic, vowing to end their three-year reign as Scottish Premier League champions.
"It's time for that to change," he said. "Everyone here wants to be champions again and to bring happiness to the fans."
Twice capped for Portugal, Mendes moved to Fratton Park from Tottenham in January 2006, having previously been with Porto.
Rangers manager Walter Smith
And he believes that his new club will benefit from his four-year experience of UK football.
"That will help," he said. "I know the game in England and the UK already, so I'm already used to the British game."
Rangers are short of options in central midfield, with skipper Barry Ferguson currently sidelined by injury, and manager Walters Smith has been quick to spend following the £7.8m sale of Carlos Cuellar to Aston Villa.
The Rangers boss expects Mendes to make an impact.
"He's very good technically and I hope he will come and improve us," said Smith. "He is a really good all-round midfield player.
"He can get a goal or two as well, so he will be a good acquisition for us."
But the capture of Mendes may cool Rangers' interest in Fulham's Steven Davis.
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.