Ben Stokes, who was voted the IPL's most valuable player, Jos Buttler and Chris Woakes all return to the England fold after starring in the Twenty20 competition.
"To have those guys back in the side is a huge boost," said Morgan.
The ODI series against South Africa begins at Headingley on Wednesday.
All-rounder Stokes became the IPL's most expensive foreigner when he was signed by Rising Pune Supergiant for £1.7m. He went on to score 316 runs - including a maiden T20 century - at a strike rate of 142.98 and took 12 wickets at an economy rate of 7.18.
He and wicketkeeper-batsman Buttler, who made 272 runs for Mumbai Indians, helped their respective teams reach the final but neither took part after being recalled by England for the upcoming ODI series.
Mumbai went on to beat Pune by one run in the final.
Bowler Woakes, meanwhile, took 17 wickets at an average of 22.7 in 13 games for Kolkata Knight Riders.
"It's a huge benefit having three match-winners come back into the team having watched them contribute so much to the IPL," said Morgan.
"Ben comes back as the competition's MVP and it's great to see him performing so well in what is the biggest domestic tournament in the world.
"Jos is one of the best in the world as well and Chris has been an important part of his side's road to the final stages."
England play two further ODIs against South Africa, at Southampton on 27 May and Lord's two days later.
Trevor Bayliss' side begin their Champions Trophy campaign against Bangladesh on 1 June.
May
24 1st ODI, Headingley (d/n) (14:00 BST)
27 2nd ODI, Southampton (11:00 BST)
29 3rd ODI, Lord's (11:00 BST)
From 1-18 June, England and South Africa take part in the ICC Champions Trophy, hosted in England and Wales.
June
21 1st Twenty20 international, Southampton (d/n) (18:30 BST)
23 2nd Twenty20 international, Taunton (17:00 BST)
25 3rd Twenty20 international, Cardiff (14:30 BST)
July
6-10 1st Test, Lord's (11:00 BST)
14-18 2nd Test, Trent Bridge (11:00 BST)
27-31 3rd Test, The Oval (11:00 BST)
August
4-8 4th Test, Old Trafford (11:00 BST)
The return of "three match-winners" from the Indian Premier League has been welcomed by England one-day captain Eoin Morgan.