Leg-spinner Rehan Ahmed will become England's youngest-ever Test cricketer when the third and final game against Pakistan begins in Karachi on Saturday, skipper Ben Stokes said.

Ahmed will be 18 years and 126 days old when the match begins, beating Brian Close who was 18 years and 149 days old when he debuted for England against New Zealand at Manchester in 1949.

"I think it's a good opportunity for us to not only look at him but for him to come in and experience what it's like to play international cricket," Stokes told a news conference in Karachi.

"It's exciting times for Rehan especially, and he was very excited when we gave him the nod that he was going to play last night."

Ahmed will replace spinner Will Jacks, while wicketkeeper Ben Foakes comes in for James Anderson, who is being rested, in two changes from the second Test in Multan.

England won that match by 26 runs to take an unbeatable 2-0 series lead.

The teenager's inclusion highlights England's bold approach to Test cricket, adopted since Stokes took over as skipper and former New Zealand skipper Brendon McCullum became head coach in May.

Stokes said Ahmed was impressive in the last English season, scoring a hundred and taking five wickets in his last first-class match.

He also impressed McCullum and Stokes in the pre-tour match in Abu Dhabi last month.

"He's got a vast array of shots. And obviously a wrist-spinner is great to be able to have in your team, especially in these conditions," he said.

Stokes hoped Karachi's National Stadium pitch would take more spin than the one used in Multan.

"We've taken a look at the wicket as well, which looks very dry, I personally think it might spin a bit more than it did in the last Test match," he said.

England are on their first Test tour of Pakistan since 2005, having long refused to tour for security reasons.

Ahmed caught the attention of cricketing giants even as a boy, bowling to an impressed Stokes in the nets at just 11 years old.

The late legendary Australian spinner Shane Warne predicted a few years later that Ahmed would be "playing first-class cricket by the age of 15".

"I think we're going to be commentating on you really soon," Warne told the youngster.

Ahmed, who has Pakistani roots like another England leg-spinner, Adil Rashid, has long focused on his dream of playing Test cricket.

"I say to every captain I play for – I'm always ready. If you want me at the death, if you want me to open the bowling, I'm ready to do it," he told reporters in October.