Spurs announced they had agreed a fee with a MLS side for the sale of the forward on Saturday.
And the USA international captain, who spent one season at White Hart Lane, was unveiled by the club before their 3-0 victory over Dallas.
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Dempsey has scored 35 goals in 99 appearances for the USA national team. He began his career with the New England Revolution in 2004, before moving to Fulham in 2007.
After six successful seasons at Craven Cottage in which he scored 50 goals in 184 league appearances, he signed for Tottenham in the summer of 2012, making 29 league appearances in his one season at the club.
"In doing something of this magnitude we had to make sure we had the right player," owner and general manager Adrian Hanauer added.
"Clint Dempsey fits that mold. Clint is a proven winner, a leader and a competitor who we believe will raise the bar for this organization on and off the field."