Somerset spinner Dom Bess has been called up for the first time, after his team mate Jack Leach broke his left thumb in the nets last week.
Bess has played 16 first-class matches, impressing with both bat and ball, and Smith said the 20-year-old had made a fine start to his career.
"With Jack Leach missing out due to injury, the selection panel wanted to invest opportunity in a young spin bowler," Smith said in a statement on the England and Wales Cricket Board website https://www.ecb.co.uk/england/men/news/691069/england-name-squad-for-first-test-against-pakistan.
"Dom's strong form, character and all-round abilities presented a compelling case for selection."
Buttler plays as opener for the Royals, but is likely to slot into England's middle order.
"The selection panel feels that this is the perfect moment to reintroduce Jos to test cricket, where he has already enjoyed some success, including a stint playing as a specialist batsman at number seven," Smith added.
"Jos is playing with great confidence and flair, and he will bring unique qualities to the test team."
James Vince has not been included in the 12-man squad following his disappointing Ashes series.
England will play two tests against Pakistan, with the second starting on June 1 at Headingley.
England squad for the first test against Pakistan:
Joe Root (Yorkshire) captain; James Anderson (Lancashire); Jonny Bairstow (Yorkshire) wicketkeeper; Dom Bess (Somerset); Stuart Broad (Nottinghamshire); Jos Buttler (Lancashire); Alastair Cook (Essex); Dawid Malan (Middlesex); Ben Stokes (Durham); Mark Stoneman (Surrey); Chris Woakes (Warwickshire); Mark Wood (Durham)
(Reporting by Simon Jennings in Bengaluru, editing by Pritha Sarkar)
