The 34-year-old free agent has been in talks with the Black Cats and a one-year deal was finalised on Thursday afternoon with the club making a formal announcement on their official website.
Manager Martin O'Neill said: "Louis is a striker whose abilities have been proven at the very highest level and he brings with him a raft of experience of top-flight football.
"I'm sure he will be a great addition to our squad in an area we recognise needs strengthening and I'm delighted we have been able to complete the deal ahead of our first game of the season."
The former France international joined Tottenham on a short-term deal from Everton in January and scored three goals in 10 Premier League appearances.
He has extensive experience in English football, scoring 112 league goals for Newcastle, Fulham, Manchester United, Everton and Spurs since joining the Magpies from Metz in 1999.
Saha's arrival relieves the pressure on O' Neill to sign a new striker having seen Asamoah Gyan leave the club on a permanent deal and Nicklas Bendtner return to Arsenal.
The club had been pursuing Wolves star Steven Fletcher but it was confirmed earlier this week that an offer in the region of £13 million had been turned down by the Championship club.