Lennon, 27, has made nine Premier League outings this season, and another eight in cup competitions.
The England international has scored 30 goals in 365 games for Spurs since his 2005 arrival from Leeds United.
"We all know what Aaron will bring to our squad with his experience and know-how, his involvement with England in two World Cups and the landmarks he has set in the Premier League," boss Roberto Martinez told Everton's website.
"At 27, Aaron will be a really important asset to our squad and he will represent a real boost in terms of attacking options from now to the end of the season. His pace and trickery will fit in well at Goodison."