“I’m thrilled to be making a one-off return to Formula One racing, and I couldn’t think of a better place to make that return than my adopted home Grand Prix: Monaco,” said the 2009 world champion at the Bahrain Grand Prix.
Honda-powered McLaren has endured a tough start to the season, with no points from two races, but the slow
He is also the last driver to win a race for McLaren, in Brazil in 2012, but cannot hope for such success this time.
"It's one of my all-time favourite racetracks," said the winner of 15 Grands Prix. "OK, I realise we won't have a realistic chance of repeating my 2009 victory, but I think we'll have an opportunity to score world championship points, which will be very valuable to the team in terms of Constructors' rankings.
"As for Fernando, I hope he not only fares well at Indy but enjoys it too."
McLaren announced earlier in the week that former double world champion Alonso would compete at Indianapolis with a car run by Andretti Autosport, last year's winners.
The team made no mention of any testing before Monaco but Button said he would use McLaren's simulator and had no fitness concerns. Button has been spending time in California, competing in triathlons and was recently disqualified for speeding during an Ironman 70.3 event.
McLaren racing director Eric Boullier said Button's return was great news.
"Jenson is a class act. He's a superb driver - fast, smooth and precise - and he won't have lost any of his competitive edge over the past few months," Boullier said. "He's always been good at Monaco. He'll do a great job for us, I'm sure of that."