Sheffield Wednesday boss Darren Moore and Morecambe’s Derek Adams were also nominated for April’s award.
When explaining the decision, Danny Wilson, who chairs the Sky Bet Manager of the Month judging panel, said: “Gareth’s Wycombe sprinted through April and snatched a play-off place with a 17-point return after seven unbeaten games.
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“Wins against play-off rivals Sheffield Wednesday and Plymouth enabled them to catapult into the top six on the final day of the season.”
Sky Sports’ EFL pundit Don Goodman added: “Wycombe saved their best until last this season and will look back on a 2-0 victory over Plymouth Argyle as a crucial part of an April run that ultimately rewarded them a place in this season’s play-offs.”
Ainsworth will now prepare his side for this month’s play-off final against Sunderland at Wembley on Saturday, May 21.
After receiving the Manager of the Month award for April, the Wycombe boss said: “April was a massive month for us, particularly with us coming back after a two-week international break and hoping to carry on momentum from a good run of results in March.
“The boys were brilliant in every department and it was a fantastic achievement for us to break into the top six, particularly with lots of teams around us picking up good results as well.
“I’m delighted to win the League One Manager of the Month award, which is testament to the hard work and focus of everyone at the training ground, including all the players and staff.”
Sunderland striker Nathan Broadhead was also nominated for the League One Player of the Month award, after scoring five times in seven appearances, which instead went to Sheffield Wednesday striker Lee Gregory
MK Dons midfielder Scott Twine and Wigan forward Will Keane were also among the nominees.