The 34-year-old lock left Leicester at the end of the season after the Premiership champions opted not to offer him a new deal.
Kay, who won 62 caps for England, is pursuing a media career and will now work as a commentator with ESPN.
"I had other options but I was keeping things open while ESPN confirmed the deal," Kay told the Guardian.
Kay was an integral part of England's World Cup-winning side seven years ago and also played every minute of every match in 2007 when they also reached the final before losing to South Africa. His career also featured two Lions caps in 2005.