The 21-year-old impressed on loan at Peterborough United in League One last season, playing 45 games and winning the players' player of the year award.
McGee has signed a three-year deal at Fratton Park.
"He's come through Tottenham's academy system and they've produced a lot of good players," assistant manager Joe Gallen told Portsmouth's website.
"It's great that we've been able to bring in a goalkeeper who's good enough now and is going to improve in the future."
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Portsmouth have signed goalkeeper Luke McGee from Tottenham Hotspur for an undisclosed fee.