The Australian defender is on loan at Seattle, but the Premier League season is set to begin in early August.
Given the MLS runs on a different schedule, Smith will be able to remain with Seattle until their season concludes.
The defender has managed five assists for the team in 19 appearances.
"We're very pleased to have worked out a deal with Bournemouth to keep Brad here through the current campaign," said Sounders FC General Manager & President of Soccer Garth Lagerwey.
"Brad has performed admirably since he arrived in Seattle and is an important piece of our current squad, so we're excited to have him here as we approach the homestretch of the season."