Scharner, 32, joins Wigan on loan from Hamburg to return to the club where he first made his name in English football.
The midfielder first signed for Wigan from Brann in January 2005, going on to make 145 Premier League appearances before a move to West Brom in 2010.
He signed for Hamburg last summer but has been restricted to only one Bundesliga start at the German club.
“It really is fantastic to be back," Scharner told the club's official website. "Wigan will always have a big place in my heart, so to be asked to come back and help the team now is something really special for me.”
Scharner is Wigan's fourth signing of the January window following Roger Espinoza, Angelo Henriquez and Joel Robles.
Roberto Martinez's side looked to be closing in on Barnsley defender Stones, 18, after Barnsley gave them permission to speak to him.
However the Toffees also came in for him and he chose Goodison. The move is worth around £3m.