Jack Redden is an Eagle after West Coast agreed to send its first-round pick to the Brisbane Lions in exchange for the midfielder.
Late on Monday, the AFL announced the two clubs had signed off on the deal late on the first day of the NAB AFL Trade Period.
West Coast held draft pick No.17, which is now in the Lions' hands.
Redden was contracted at the Lions until the end of 2016 when he was due to become a restricted free agent.
The 24-year-old requested a trade last month and soon afterwards nominated West Coast as his preferred new club.
West Coast football manager Craig Vozzo said he was delighted to have the deal done.
"We are thrilled and excited to have a player of Jack’s quality and experience coming to the club and he will add another dimension to our midfield," Vozzo said. "We look forward to Jack joining our club and playing his part in our vision for sustained success.
"He is a strong-bodied inside midfielder and aside from being an impressive young man, he brings with him attributes that will strengthen our list. We look forward to welcoming Jack and his fiancée Aimee to the club."
The Lions are also set to farewell ruckman Matthew Leuenberger, with Essendon expected to lodge an offer for the restricted free agent on Tuesday.
The Lions will then have three days to match the Bombers' offer.
Redden played 129 games in seven seasons at the Gabba after being drafted with pick No.25 in the 2008 NAB AFL Draft.
The South Australian twice finished third in the Lions' best and fairest award, in 2011 and 2013.