The two-time Formula One world champion returns to the fabled US race after failing to qualify for the event last year.
The 38-year-old Spaniard is trying to emulate the feat accomplished by the late Graham Hill, the only driver to win the Monaco Grand Prix, Le Mans and Indy 500.
Alonso has won both at Monaco and Le Mans, the 24-hour endurance race, twice.
“I am a racer and the Indy 500 is the greatest race in the world,” Alonso said in a team statement.
“I love the incredible fans who make it so special for all of us drivers and make me want to come back.”
It will be Alonso’s third Indy 500 participation. He qualified fifth for the 2017 edition and led for 24 laps before he was forced to retire due to engine failure.
Alonso finished 13th on his Dakar Rally debut in January, nearly five hours behind winner Carlos Sainz.
Alonso came second in one stage but his first attempt at the Dakar was a bruising affair as he suffered a double rollover in the 10th stage after hitting a dune at an awkward angle.