Newcastle seal deal for Obertan
"His best years are ahead of him which is exactly what we want at this club and with the backing of our magnificent fans I'm sure he will prove an excellent signing for us," Newcastle manager Alan Pardew said in a statement.
Obertan, 22, struggled to make an impact at Old Trafford after joining from French Ligue 1 side Girondins Bordeaux in 2009, making only 15 appearances last season.
The former French Under-21 international said he was looking forward to playing more regularly at Newcastle.
"I spent two good years in Manchester but it was a bit difficult with the competition and I really needed a club where I could play more games," Obertan said.
"I know it won't be easy to play each game here because there's a good group, but I want a fresh start in my football."
Obertan will go straight into Newcastle's squad for Saturday's opening league match at home to Arsenal.