McManus is the first player to join the club since the appointment of new head-coach Rehanne Skinner, who worked with the 28-year-old in her former role as England assistant manager.
“I worked with Rehanne recently when she was assistant coach for England and I’m looking forward to working with her again,” said McManus. “I’m excited to be here and can’t wait to get started.”
McManus joined the Red Devils in 2019 from neighbours Man City, where she made over 110 appearances in two spells over more than a decade.
She has made 25 appearances for Casey Stoney’s side but has struggled for minutes this season and wants regular football to maximise her chances of being picked for Team GB at next summer’s Olympics.
McManus, who also had a spell at Sheffield Ladies, was City’s longest-serving women’s player and was part of the side that won a WSL title, two Women’s FA Cups and two Continental League Cups, as well as featuring in two Champions League semi-finals.
“I’m really excited to be joining Tottenham Hotspur, a big club with big ambitions,” added McManus.
“The team is in great form, winning three games on the bounce, and hopefully we can continue to build on those performances in the next few games and get into the top half of the table.”
Elsewhere, England midfielder Jill Scott has rejoined former club Everton on loan from City until the end of the season to increase her chances of being picked for the Games.