Bairstow arrived in Sri Lanka as England’s first-choice wicketkeeper but was ruled out of the series opener in Galle due to injury and overlooked in Kandy following Ben Foakes’ fine debut with the gloves.
He will return to the XI as a specialist batsman in Colombo tomorrow (4.30am start) alongside returning seamer Stuart Broad, with England swapping out Sam Curran (side strain) and James Anderson (rested) as they bid for a clean sweep of wins.
The 29-year-old has also been told he will bat at first wicket down, a crucial position that has not been satisfactorily filled since the days of Jonathan Trott.
In the past five Test matches Root, Moeen Ali and Ben Stokes have all started as the designated No 3, while the use of a nightwatchman saw Keaton Jennings bat there in the second Test and Jos Buttler was publicly considered for the job too.
England have talked up the malleability of their team in Sri Lanka, emphasising the willingness of individuals to perform a variety of tasks, but a successful audition by Bairstow would lend a welcome air of permanence to the top order.
“One thing we all know about Jonny is whenever he’s got a point to prove or is up against it, he generally comes out and does something pretty special,” said Root.
“Hopefully we see that with Jonny this week – that determination and drive to really hammer that spot home for himself. It’s an opportunity for him to try and nail that spot down and he’s more than capable of doing it.
“At the minute that (keeping wicket) is not an option for him in this team and I think it’s a really good opportunity for him to take his batting to another level.
“In the last couple of years he’s been statistically one of the top 10 players in the world in Test cricket so it would be nice to see him really grab No 3 by the scruff of the neck and use it as an opportunity to start really consistently scoring big runs in this format.
“There’s so many different combinations that we could go with that look extremely strong in all conditions.
“It would be, obviously, in terms of having a settled batting line-up, especially a top six – it would be ideal to get that settled down.”
There are no concerns over how Stokes will take his move back down to No 5 after precisely one innings, of 19, in the top three.
Root indicated the all-rounder’s workload with the ball, which could include new-ball duties this week in the absence of Curran and Anderson, meant he had a more natural home further down the card.
“I think that’s his preferred position. Long-term as well, he’s going to be bowling more in the English summer,” he explained.
“Although it wouldn’t be impossible for him – he’s a very fit guy, very able to do so – it might be a better formula to have him in the middle-order.
“He is so valuable to this team and the white-ball team too, because he balances it out brilliantly.
“He is someone who always wants to be involved. He wants the ball, he wants to be bowling and he wants to try and influence what is going on in the field.
“They are the characters you want in the dressing-room and they drive standards. People look at them and say ‘I want to be like that’. He’s so valuable.”
Record wicket-taker Anderson will make way for his longstanding new-ball partner Broad after admitting to feeling “like a spare part” on spinning pitches in Galle and Kandy.
For Anderson, it represents an early end to a challenging trip. The 36-year-old has sent down a total of 41 overs in four innings on unwelcoming tracks with his solitary dismissal coming when he found Dimuth Karunaratne’s edge with his second ball of the series.
“Broady’s going to play instead of me. The thinking is that with the series sewn up it’s an opportunity to rotate,” he said.
“Joe Root told me this morning. I had a feeling it might be the case. You don’t want to miss a Test – I never like it – but I understand the reasoning behind it.
“We’re going to the West Indies (in the new year) and with a view to that, I think the feeling is they want Broady to get some Test cricket under his belt. So it’s going to be a week off.
“It’s been a frustrating trip for me really because you want to contribute to the wins and I feel like I’ve tried my best but it’s not really been a series for the seamers.
“I feel like a bit of a spare part but I think that’s just the nature of playing cricket here.
“As frustrating as it’s been for me personally, it’s been brilliant to be a part of such a great series for the team.”
It is a measure of England’s growing confidence that they feel emboldened do battle without Anderson’s knowhow and experience, not to mention his 565 Test scalps, though few stand-ins in history can have boasted more than Broad’s tally of 433.