The 28-year-old midfielder passed a medical at Spurs' Chigwell training ground before putting the finishing touches to his transfer from Everton for a fee believed to be between ¦pound;2.5million and ¦pound;3million.
Earlier confirming his destination on his Twitter account, Pienaar said: "To end speculation I am going to Spurs. I've had brilliant years at Everton and it will always be a special place in my heart."
He later added: "I can also confirm I'll be jersey number 40."
Confirming the completion of the transfer on their official website, www.tottenhamhotspur.com, Spurs said in a statement: "We are delighted to announce that we have reached agreement with Everton and Steven Pienaar for the player's transfer to the club."
Pienaar could make his debut in Saturday's Barclays Premier League game at Newcastle providing his work permit comes through in time.
Tottenham beat Chelsea to land Pienaar, who failed to agree personal terms with the champions. That does not appear to be a problem with Spurs, who nevertheless risked missing out on the South Africa star by refusing to meet Everton's asking price.
But the clubs came to an agreement last night, with some reports claiming Tottenham had matched Chelsea's ¦pound;3million bid for the player and others suggesting a compromise figure of around ¦pound;2.5million had been reached.
Once all the paperwork is complete, Pienaar will officially become the north Londoners' second January signing, with international team-mate Bongani Khumalo having already penned a pre-contract agreement.
Everton decided to sell the influential playmaker, rather than lose him on a free transfer when his contract expired in the summer.
Source: PA
Source: PA