John, also a midfielder, is the second player to sign today after Lewwis Spence.
Mousinho is Amersham based and has many friends who are Wycombe fans and he joins on a free transfer.
"I'm a hard-working central midfielder so hopefully there'll be a lot of action and I'll bring some quality as well," he told www.wwfc.com
"First and foremost, we want to get back into League One so promotion has to be the main ambition this year and a club with this ambition will be aiming higher than League One after that."