Boyd's manager Liam Pickering confirmed Boyd would receive a seven-year deal at the Bulldogs, and it's rumoured to be worth more than $6 million.
It represents an embarrassing backdown from the Giants chief executive David Matthews - who had last week vowed Boyd would not be traded under any circumstances.
However the expansion club will emerge with Griffen and draft picks 4, 6 and 7 - which are now likely to be used to prize the number one selection from St Kilda.
Matthews told Trade Radio on Wednesday that GWS would immediately negotiate with the Saints, and hope to reach a deal before Thursday's 2pm deadline.
Shortly after, St Kilda list manager Ameet Bains declared his club would be open to offloading pick No.1, as it has maintained thrououghout the trade period.
"We would entertain trading the No.1 pick for either a combination of those selections, or one of those picks and a player," Bains told Trade Radio.
"If GWS want to speak to us, we will have a discussion in due course.
"History shows that pick one brings a very special player. We'd be reviewing any offer in that context."
The Giants could draft a replacement tall forward in Peter Wright if they retain pick four.
However, the club is more likely to select midfielder Christian Petracca if it lands the No. 1 pick.
Twelve ex-GWS players have now found another AFL club in three years.
-Taylor Adams
- Jack Hombsch
- Dom Tyson
- Josh Bruce
- Anthony Miles
- Sam Darley
- Kurt Aylett
- Shaun Edwards
- Jono O'Rourke
- Kristian Jaksch
- Mark Whiley
- Tom Boyd
Matthews said the club had changed its position on Boyd because the trade was "in the best interests of the club".
"First, the Bulldogs have made a revised and attractive offer which now includes their first draft pick (six), an elite player in Ryan Griffen and salary cap assistance in relation to his contract," he said.
"Second, our coach Leon Cameron has consulted the leadership group and they have agreed they want a united and loyal playing group heading into an important season in 2015.
"Third, as a club we are proud to represent Western Sydney and Canberra and it's critical that our players share that value. Clearly Tom doesn't and the best course of action is for him to leave the club.
"We believe this is an excellent trade in the best interests of the club and gives us the best possible chance of achieving success in the coming seasons.
"It significantly strengthens our playing list and gives us picks 4, 6 and 7 in next month's draft which can also be traded.
"We are delighted to have Ryan Griffen at the club. He is not only a great talent but a person with strong values and brings more experience and maturity to the list."
Tom Boyd and Ryan Griffen boom AFL trade complete
