The 39-year-old took over as caretaker boss following the dismissal of Gary Waddock in September but the club have decided to offer the job to Ainsworth until the end of the season.
"I'm delighted and honoured to be the manager of Wycombe Wanderers," Ainsworth told the club's official website. "The club has a big history of successful managers and I will be giving it my all to join that list."
Joint chairman Don Woodward added: "We knew he would be a frontrunner for the job from the moment we placed him in caretaker charge, but his outstanding attributes really came to the fore over the last seven weeks and we feel now is the right time to seal our commitment towards him as the next manager of this proud football club."
Wycombe are currently one spot above the relegation zone.