The 70-year-old Rothwell, who lives locally in Saddleworth, became the oldest person to row a boat solo across the Atlantic so clearly welcomes a tough challenge.
Owners Abdallah Lemsagam and Simon Blitz have agreed to sell to Rothwell, who has also secured a deal to buy the Boundary Park stadium.
The Latics were relegated from the Football League for the first time in 115 years last season amid angry fan protests at how the club was being run.
A statement on Oldham's website read: "Following the conclusion of negotiations with Abdallah Lemsagam and Simon Blitz, the sale of Oldham Athletic AFC can now be confirmed.
"We are also at an advanced stage to purchase Boundary Park stadium, hopefully within the course of the next week.
"Headed by our new chairman, Frank Rothwell, the Oldham-based owner and founder of Manchester Cabins which has long-standing local ties, the deal will ensure that the club and stadium will be consolidated under one ownership.
"This is a significant and hugely exciting development in the proud history of Oldham Athletic and ensures the club can now approach the new season and beyond with a genuine sense of anticipation."
The Latics begin their National League campaign against AFC Fylde on Saturday.