According to the Mail Online, the Portuguese has put pen to paper on a contract until the end of the 2022/23 season on a salary of £15 million a year.
That is almost twice as much as his predecessor was paid by the Premier League club.
Pochettino was sacked after a disastrous start to the Premier League season that has left them 14th in the table with just three wins in 12 games.
Mourinho has won three Premier League titles over two spells with Chelsea, but has been out of a job since leaving United in December last year.
“I am excited to be joining a club with such a great heritage and such passionate supporters,” he said.
“The quality in both the squad and the academy excites me. Working with these players is what has attracted me.”
Spurs chairman Daniel Levy said: “In Jose we have one of the most successful managers in football.
“He has a wealth of experience, can inspire teams and is a great tactician. He has won honours at every club he has coached. We believe he will bring energy and belief to the dressing room.”
A statement from the club added: “Jose is one of the world’s most accomplished managers having won 25 senior trophies.
“He is renowned for his tactical prowess and has managed FC Porto, Inter Milan, Chelsea, Real Madrid and Manchester United.
“He has won a domestic title in a record four different countries (Portugal, England, Italy and Spain) and is one of only three managers to have won the UEFA Champions League twice with two clubs, FC Porto in 2004 and Inter Milan in 2010.”
Pochettino was dismissed after five-and-a-half years in charge, less than six months after he took Spurs to the Champions League final,
Mourinho’s first match in charge will be the London derby away to West Ham on Saturday and they are due to play United at Old Trafford on December 4.
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