Both came off the bench to play during the second half of last week's match against defending European champions Munster and have now been promoted to the starting XV.
Geordan Murphy has recovered from an eye injury to reclaim his place, while Julian White is at tighthead prop, with Martin Castrogiovanni moving across to loosehead. James Hamilton, who joins up with the Scotland squad for the first time next week, is in the second row alongside Ben Kay after injury to Leo Cullen.
"With Harry, Andy and Julian, I am rewarding their efforts in the second half of last week's game, though you also have to acknowledge the guys who put in such a lot of hard work in the first half," said Tigers head coach Pat Howard.
"Leo Cullen was touch and go whether he played against Munster - he has been carrying a few knocks - but he battled on and played very well. We have four second rows who are very, very close and they are all performing well, so I have no worries in bringing Jim in this time.
"It was a tough call on leaving out Johne Murphy because he has done well, but Geordan had done nothing wrong before he was injured in the run-up to last weekend."
Brett Deacon replaces Jordan Crane on the bench as the only other change to last weekend's matchday 22.
"It is a chance for Brett, he offers something a little different," added Howard.
"This is a huge game for the club, it is going to be a great measure of our side against a Cardiff team that is playing well and got off to a winning start in the Heineken Cup. They had a good win over Bourgoin and they also showed they are a good side with their performance against Wasps in the EDF Energy Cup.
"I think our players viewed last week's result as a real missed opportunity, but I was really proud of how they never gave in. We are going to play against a good side at their home on Sunday, just as Munster did last weekend, and I am sure the squad is up for this challenge."
Tigers, who will wear their green kit in Cardiff, have confirmed that the Millennium Stadium roof will be closed on Sunday.
Leicester Tigers team:
15 Sam Vesty
14 Geordan Murphy
13 Ollie Smith
12 Daryl Gibson
11 Tom Varndell
10 Andy Goode
9 Harry Ellis
1 Martin Castrogiovanni
2 George Chuter
3 Julian White
4 James Hamilton
5 Ben Kay
6 Louis Deacon
7 Lewis Moody
8 Martin Corry (capt)
Replacements
16 James Buckland
17 Marcos Ayerza
18 Shane Jennings
19 Brett Deacon
20 Scott Bemand
21 Paul Burke
22 Seru Rabeni
