Purnell, a former team principal of the Jaguar Formula One team and ex-technical advisor to world motorsport's governing body the FIA, will arrive as head of technical development of the Great Britain team.
British Cycling is famed for its attention to detail and Purnell will work across all aspects of technology – from improving data analysis to assisting the coaches with the development of organisational software and tools to optimise rider performance – alongside Chris Boardman who will continue to act as a consultant.
Olympic champion Boardman and Matt Parker, the head of marginal gains, were key to Britain's success at the 2008 and 2012 Olympics, when seven gold medals were won on the track in each Games.
And Purnell's appointment shows Britain's desire to continue to look for marginal gains ahead of Rio 2016 despite Boardman stepping back from his role and Parker's move to the Rugby Football Union, where he is now working with the England team.
"We are very fortunate to have someone of Tony's experience and ability to work with the riders and coaching staff," Brailsford said.
"We know that sustaining success is among sport's greatest challenges and the recruitment of Tony is a significant step on the road to Rio."