Timo Werner began his career at Stuttgart before joining RB Leipzig in 2016
The 27-year-old's move includes an option to be made permanent in the summer.
He bolsters Tottenham's forward options with Son Heung-min away with South Korea for the Asian Cup and James Maddison sidelined with injury.
"I spoke with the [Spurs] manager [Ange Postecoglou] and it was a really good talk," said Werner.
"He gave me straight away the feeling what I need to join a club and what I want to feel when you talk to a manager.
"Also, that tactics and style, how he wants to play. For me, I thought straight away that it fits perfectly."
Werner has Premier League experience with Chelsea after joining the Blues in a £45m move from Bundesliga club Leipzig in 2020.
He scored 23 goals in 89 appearances for Chelsea, winning the Champions League, Super Cup and Club World Cup, before returning to Leipzig in 2022.
He has scored two goals in 14 appearances this season but missed Saturday's friendly with St Gallen because transfer talks were taking place with Tottenham.
Werner has 57 Germany caps but last played for his country in a friendly defeat by Belgium in March 2023.
His move is subject to international clearance but Werner could be available when Spurs play at Manchester United in the Premier League on Sunday, 14 January (16:30 GMT).
Tottenham are fifth in the top flight, six points behind leaders Liverpool.
"I hope I can be the best player I can be here," added Werner. "I can play every position up front - that's one of my strengths.
"My aim is to fight for another win in this league and also maybe for titles.
"When I joined my old club [Chelsea] I also said I wanted to be a winner and win titles. In the end we won the Champions League, so I think it should not be too bad to also win titles and to win something."
-- Courtesy of BBC Sport