Healy, who still holds the record as Northern Ireland's leading goal scorer, played for Leeds between 2004 and 2007.
He was also the club's top scorer for all three seasons.
Glenavon player-manager Gary Hamilton said it was an honour to have Healy join the team for the fixture on 30 July.
"It is great news for both the club and the players who will have the honour of playing with him that David has chosen to join us to celebrate our 125th anniversary," he said.
"Glenavon will be the first Irish League club, of course, that he will have played with.
"Despite his many successes, David has always remained grounded - he has never forgotten where he came from and is a credit to himself and his family. He is always ready to help out Northern Ireland football in whatever way possible.
"It is a measure of the man that he accepted without hesitation our offer to play and, as I said, it will be an honour to have David here on 30 July."