Pandhare, who retired from Maharashtra Engineering Training Authority, Nashik, yesterday, joined AAP in presence of its Maharashtra convener Anjali Damania at a public meeting.
Pandhare had last year written to Chief Minister Prithviraj Chavan, exposing alleged scams in various irrigation projects.
He told reporters that he was ready to contest Lok Sabha elections if the party asked him to.
Pandhare said he joined politics to "remove corruption from top to bottom".