Freeland has signed a three-year deal with NBA side Portland Trail Blazers, who he first spent time training with six years ago.
And the 25-year-old's representatives are currently negotiating a 1.5 million euro release clause in his contract with Spanish ACB side Unicaja Malaga.
Once finalised he will be the second NBA player in the British team, alongside Chicago Bulls All-Star Luol Deng. In addition both Pops Mensah-Bonsu and Rob Archibald have experience in the world's top league.
"This is fantastic news for Joel and in our view is richly deserved," said British Basketball performance director Chris Spice.
"Joel is a great player who continues to make an outstanding contribution to the GB programme. We wish him well in this new challenge."
Freeland made his debut for Chris Finch's Great Britain side in 2006 and was outstanding at last year's EuroBasket.
He is expected to miss a few days training but will be back for next week's match against the USA in Manchester.
Great Britain will start their first Olympic basketball campaign since 1948 with a group game against Russia on July 29.