The trio will now remain with the province until at least June 2019 after putting pen-to-paper on two-year extensions to their original deals.
Munster have been in talks with all three for the last month as they attempted to tie down the Greencore Munster Rugby Academy products.
Director of rugby Rassie Erasmus was delighted with the news and believes it is crucial for their future plans as they look to provide plenty of competition for places.
Erasmus said: “It’s great to see players who have come through our academy system commit their future to Munster.
“Jack (O’Donoghue) and Ronan (O’Mahony) are among our standout players this season, and while injury has kept Alex (Wootton) side-lined of late, he really impressed when opportunity presented itself earlier in the season and is an exciting prospect.
“It’s good to have all three on board as we continue to build our squad depth.”