Tottenham chairman Daniel Levy, announcing Mourinho's arrival, 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."
Mourinho said: "I am excited to be joining a club with such a great heritage and such passionate supporters.
"The quality in both the squad and the academy excites me. Working with these players is what has attracted me."
A Spurs statement read: "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.
"He is also a three-time Premier League Champion with Chelsea (2005, 2006, 2015)."
The 56-year-old Portuguese won three Premier League titles over two spells in charge of Chelsea and returned to England to manage Manchester United in 2016.
He was sacked last December following a poor run of results and has been out of work since, most recently working as a pundit for Sky Sports.
Pochettino was dismissed after five-and-a-half years in charge, less than six months after he took Spurs to the Champions League final, with the club lying 14th in the Premier League table after the opening 12 matches.
Mourinho, who also managed Porto, Real Madrid and Inter Milan, has turned down a number of opportunities to coach abroad, including with clubs in China, Spain and Portugal, since his Old Trafford exit.
His first match in charge will be the London derby away to West Ham on Saturday.
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