Subject to visa, the 25-year-old front-row will join the club this summer after a final season in Super Rugby, with the season running from February to July.
Edinburgh Rugby head coach Michael Bradley said: "We're delighted to have signed WP Nel for the next three seasons; a player of the calibre, experience and expertise that we seek to attract to the club and to serve our ambitions to put Edinburgh Rugby among the top clubs in Europe.
"He has a lot of experience for a 25-year-old prop and will bring a huge amount to our performance on the pitch and to the development of the talented young props we have at the club."
Nel goes into the 2012 Super Rugby season with three year's experience of the southern hemisphere's top club rugby division, having made 32 appearances since his debut against the Waratah's at the tail end of 2009.
He then starred in the club's journey to the Currie Cup final in which his highlight was undoubtedly a semi-final overpowering of Natal Sharks' South Africa internationalist Tendai 'the Beast' Mtawarira.
These fledgling performances paved the way for Nel's selection for the Cheetah's narrow loss to the British & Irish Lions in 2009 (24-26), where he packed down against soon-to-be colleague Ross Ford, before starting as the only non-capped player in the Barbarians' win over the All Blacks at Twickenham (25-18).
Since then Nel's stock has continued to rise as he established himself as an ever-present in the Cheetahs' front-row, starting all of the 29 matches in the 2010 and 2011 seasons.
Looking ahead to his summer switch Nel said: "My experience at the Cheetahs has been fantastic and I can't thank coach Naka Drotske enough for all that he has done for me but when I got the chance to go to Edinburgh Rugby, it was an opportunity to gain new experience and develop my game even further.
"Edinburgh Rugby play a fantastic brand of rugby and I'm really looking forward to lining up alongside some of their world-class players and living in a great city like Edinburgh.
"To be involved in that set-up and experience northern hemisphere rugby and conditions can only improve my game in two great competitions - the Rabodirect PRO12 and the Heineken Cup - and I'm certainly looking forward to the challenge."
Edinburgh Rugby Chief Executive, Craig Docherty, said: "The signing of WP Nel is a clear statement of intent from Edinburgh Rugby as we look to retain and recruit the right players that will help us build on the many strides made this season and to ensure that we continue this momentum into future years.
"Nel is a world-class performer as he has shown in one of the toughest club rugby environments, the southern-hemisphere's Super 15 and for the Barbarians, in that famous win over the All Blacks.
"I'm sure he'll be big hit with supporters and will serve as an excellent addition to the club as we ramp up our search for silverware."
WP NEL
Date of Birth: 30/04/86 (25) - in Loeriesfontein, Northern Cape
Position: Tighthead Prop
Height: 1.82m (5'10")
Weight: 120kg (18st 9lb)
Honours: Barbarians v All Blacks, Twickenham (2009)
2011: Free State Cheetahs: Super Rugby and Currie Cup
2010: Free State Cheetahs: Super Rugby and Currie Cup
2009: Western Province: Vodacom Cup; Free State Cheetahs: Super Rugby, Currie Cup, v British Lions
2008: Western Province (Vodacom Cup), Boland (Currie Cup)
2007: Western Province (Under-21)
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