Pietersen was axed by the England and Wales Cricket Board (ECB) in February last year, but incoming ECB chairman Colin Graves has suggested a return to county cricket would enhance his chances of an England recall.
He agreed a release from the majority of his contract with Indian Premier League side the Sunrisers Hyderabad on Tuesday and will therefore be available to play for Surrey from the start of the county season in April.
"I'm absolutely thrilled to be back at Surrey," Pietersen, who was de-registered by Surrey at the end of last season, told the club website.
"It's a club very close to my heart and (director of cricket) Alec Stewart, (coach) Graham Ford and everyone at the club has been exceptionally supportive.
"There is a fantastic group of lads here, and I hope we can deliver what the great Surrey fans want to see — lots of runs and comprehensive victories."
Stewart added: "A Kevin Pietersen with ambitions to play for England and a real determination to score big runs for Surrey will be a huge asset to us."
Surrey begin the 2015 County Championship season with a match against Glamorgan in Cardiff that starts on April 19.
Pietersen, 34, has agreed to sit out the Sunrisers' entire league programme, but he could be recalled if they reach the IPL knockout phase, which runs from May 19-24.
The South Africa-born batsman is England's all-time leading run-scorer in all formats and he reiterated his desire to end his international exile in a statement on his personal website on Tuesday.
"I've never made any secret of my overwhelming desire to once again represent England and I'm going to do everything in my power to earn a recall to the international set-up," he said.
"To once again put on that England shirt would be a privilege and an honour, but now I have to focus on performing domestically and give myself the best possible chance of meriting selection."
However, despite Graves's comments, other figures in the England hierarchy have played down the prospect of a comeback for the outspoken batsman.
National selector James Whitaker said last week that Pietersen was "not part of our plans", while captain Alastair Cook described the chances of his former team-mate making a comeback as "very unlikely".
Pietersen was dropped after England's 2013-14 Ashes series whitewash in Australia, with ECB managing director Paul Downton citing his "disengagement" with his team-mates during the last Test in Sydney.
He subsequently released an autobiography in which he alleged that a bullying culture had taken root in the England changing room.
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