The defending champions bowled Ireland out for 259 in 49 overs before openers Shikhar Dhawan smashed 100 and partner Rohit Sharma 64 as India chased down the target in 36.5 overs on a batting-friendly pitch at Seddon Park.
The pair shared an Indian World Cup record opening stand of 174.
Ireland, who batted after winning the toss, owed their total to a run-a-ball 75 from Niall O'Brien, while skipper William Porterfield made 67.
Paceman Mohammad Shami finished with 3-41.
This victory ensured India, already in the last eight, finished at the top of Pool B while Ireland will likely need a win against Pakistan in their last pool match in Adelaide on March 15 to reach the quarter-finals.