Giggs, who made his United debut in March 1991, has made a club record 898 appearances, scoring 162 goals.
"When I signed my first contract, I never thought I'd be able to play at United for 22 years but I feel good and I know I can still contribute to keeping the team pushing for honours," Giggs said in a statement.
"Winning the club's 19th title [last season] was a great feeling but this club is all about what we do next and I'm really pleased I can be part of that."
The former Wales international has won 12 Premier League titles, four FA Cups, three League Cups and two Champions League winners medals.
While he is no longer an automatic starter and has moved from the wing to a more central role, he is nevertheless often turned to for key games.
He is also the only player to score in every season since the Premier League replaced the old first division in 1992.
"Ryan is a marvellous player," manager Sir Alex Ferguson said in a statement.
"In many ways, he epitomises all my teams here at United; he has constantly re-invented himself, adapted to the changing nature of the game and retained that desire and hunger for success.
"In every training session and match, he is the example for others to follow. The young players in the dressing room have a great chance to learn from a player who will continue to break records that anyone in the game will find hard to beat."
