The 34-year-old former England captain and batsman has made no secret of his hopes for an international recall having being sacked by the England and Wales Cricket Board (ECB) last year.
Pietersen, who has been partly released from his commitments with Indian Premier League (IPL) outfit Sunrisers Hyderabad, will be available for all forms of cricket, starting with Surrey's opening county championship fixture on April 19.
"I'm absolutely thrilled to be back at Surrey. It's a club very close to my heart and Alec Stewart, Graham Ford and everyone at the club has been exceptionally supportive," Pietersen said on Surrey's website.
"There is a fantastic group of lads here and hopefully we can deliver what the great Surrey fans want to see -- lots of runs and comprehensive victories."
Pietersen, who scored 8,181 runs in 104 tests for England and also won 136 one-day caps, was sacked after England's 5-0 Ashes whitewash in Australia last year.
Incoming ECB chairman Colin Graves hinted this month he could be recalled if he "scores a lot of runs" for a county although national selector James Whittaker said last week the swashbuckling right-hander was not in his plans.
South Africa born Pietersen himself said this month it would be a "privilege and an honour" to play for England again.
Playing for Surrey will provide Pietersen with the perfect showcase as the home Ashes series against Australia looms.
Since his last England appearance, in the Sydney Ashes Test in January 2014, he has only played Twenty20 cricket.
"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's director of cricket Stewart said.
(Reporting by Martyn Herman; editing by Justin Palmer)
