Hugo Keenan has won his fitness race and will start for Ireland in their Guinness Six Nations clash with England on Saturday (4.45pm, live on RTÉ2 and RTÉ Player).
The 27-year-old Leinster full-back, who will earn his 39th cap, missed the win over Wales two weeks ago after injuring his knee against Italy on 11 February.
Keenan’s inclusion is the only change in the starting XV to the side that beat Wales 31-7, with Ciarán Frawley dropping to the bench.
“I think it would be a boost for any side in world rugby, he’s a world-class full-back,” Farrell told reporters on Thursday morning.
“It’s testament to him and it’s no shock to us that he’s been able to get himself back to this position to be involved this weekend.
“He’s been unbelievably diligent over the last few weeks to make that happen.”
Meanwhile, Farrell confirmed that lock James Ryan has been ruled out for the rest of the tournament.
He said: “He’s injured, he got injured yesterday in training, just a freak accident really, just a reaction, reaching out for a tackle that was non-contact and he’s injured his bicep.
“He won’t be available for the remainder of this Six Nations.”
Iain Henderson comes on to the bench having missed the last game due to a toe injury picked up on Ulster duty.
Ireland can wrap up the championship with a bonus-point win at Twickenham after claiming maximum points in their three games to date, against France, Italy and Wales.
Prop Finlay Bealham returns to the squad in place of Oli Jager, who won his first cap against Wales, and has a “niggle in his knee”.
There is no place in the squad for Garry Ringrose, who has recovered from a shoulder injury suffered in mid-January.
With Farrell opting for a 6:2 bench split, the versatile Frawley gets the 23 shirt.
“He’s fit and he’s well, he’s trained all week,” said Farrell of Leinster centre Ringrose.
“He’s done all the contact work necessary to be available. It’s just circumstances.
“Garry knows exactly. I had a chat with him yesterday and he was smiling in the fact that it’s just circumstances.
“He knows what I think about him as a rugby player and his comment to me was that he’s been on the good side of circumstances so many times as a player as well so he understands.”
James Lowe and Calvin Nash retain their places on the wings, while Bundee Aki and Robbie Henshaw start in the centre.
Jack Crowley and Jamison Gibson-Park are the starting half-backs.
The front row also remains unchanged with tighthead Tadhg Furlong set for his 75th cap, lining up beside hooker Dan Sheehan and loosehead Andrew Porter.
Second rows Tadhg Beirne and Joe McCarthy combine again with Farrell full of praise for the duo.
“They are very different, aren’t they?” he said.
“I suppose that’s the balance of a good second-row partnership. Tadhg is doing a great job of calling the lineout, he’s nice and composed as far as that is concerned.
“It adds different skills to the dynamics of our team, obviously in comparison to Joe, who is mastering the art of tighthead lock and the dark arts of causing as much havoc as he possibly can.
“He is learning that pretty quickly at the minute. I’m sure there are things he would love to get better at from the Welsh game, and he gets another chance to prove that.”
Back rows Peter O’Mahony, Josh van der Flier and Caelan Doris complete the pack.
Rónan Kelleher, Cian Healy, Bealham, Henderson, Ryan Baird and Jack Conan are the forward replacements, with Conor Murray and Frawley covering the back division.
Asked about the bench split, Farrell (above) said: “A bit of everything really. It’s where the squad is at, where the individuals within the squad are at and what benefits us against the opponent but more importantly what’s best for Ireland, so we take each game on merit and who’s fit and who’s not.
“The whole time you guys see a fit squad on paper but there’s always something going on in the background with niggles or game time or he needs looking after, or everyone could be 100% fit and raring to go, but that’s not always the case, so you take each week, and each day really, as it comes.”
Meanwhile, Steve Borthwick has made three changes in personnel and one positional switch in his side with Immanuel Feyi-Waboso will make his first start for England.
Scrum-half Alex Mitchell and lock George Martin also return to the side.
Ireland: Hugo Keenan; Calvin Nash, Robbie Henshaw, Bundee Aki, James Lowe; Jack Crowley, Jamison Gibson-Park; Andrew Porter, Dan Sheehan, Tadhg Furlong; Joe McCarthy, Tadhg Beirne; Peter O’Mahony (capt), Josh van der Flier, Caelan Doris.
Replacements: Rónan Kelleher, Cian Healy, Finlay Bealham, Iain Henderson, Ryan Baird, Jack Conan, Conor Murray, Ciarán Frawley.
England: George Furbank; Immanuel Feyi-Waboso, Henry Slade, Ollie Lawrence, Tommy Freeman; George Ford, Alex Mitchell; Ellis Genge, Jamie George (capt), Dan Cole; Maro Itoje, George Martin; Ollie Chessum, Sam Underhill, Ben Earl.
Replacements: Theo Dan, Joe Marler, Will Stuart, Chandler Cunningham-South, Alex Dombrandt, Danny Care, Marcus Smith, Elliot Daly.
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Watch England v Ireland in the Guinness Six Nations on Saturday from 4pm on RTÉ2 and RTÉ Player, follow a live blog on rte.ie/sport and the RTÉ News app and listen to live commentary on RTÉ Radio 1
Watch Wales v France on Sunday from 2.30pm on RTÉ2 and RTÉ Player
