Roy managed scores of one, eight and four in recent one-day international series against South Africa but Morgan ruled out tinkering with the opening partnership.
"The decision will remain the same throughout the tournament. Jason Roy is part of our strong opening partnership with Alex Hales. He'll definitely play," Morgan said.
Morgan's faith in Roy means Jonny Bairstow, who scored three fifties in his last four ODI knocks, will not earn selection unless a team mate is injured.
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
"I cannot see it changing. If we want our players to play cagey or without freedom, yes, we would change things and probably half of us wouldn’t be here," Morgan said.
"Jonny will miss out unfortunately. It's been the case like that for the last couple of years.
"He's been very good when he's come in, but each and every one of us within the batting department has had ups and downs over the years.
"And one of the strongest parts of reinforcing the way that we play, and the freedom in which we play with, is backing that up with selection."
Hosts England take on Bangladesh in the opener of the eight-team tournament on Thursday.
(Reporting by Amlan Chakraborty in New Delhi; Editing by John O'Brien)
