The Nigeria striker, 28, “deposited the sum of money required to meet his release clause according to the regulations of the Professional Football League,” the Spanish Liga club announced in a statement.
Newspaper El Pais said that clause was in the region of three million euros, the equivalent of a year’s salary for the former Inter Milan, Newcastle, Wolfsburg and Rubin Kazan striker.
It brings an end to a protracted transfer saga, which was initially agreed in principle last month but delayed as Levante held out for the full release clause.
"It's great to finally get it sorted out," Martins told BBC Sport. "It had been talked about for a few weeks so it's nice to know where I stand.
“I can't wait to meet the players, fans and officials of Seattle Sounders."
Martins scored seven Liga goals in 21 matches since joining Levante on a free transfer from Rubin in the summer.
The Valencia-based club were reluctant to let him leave mid-season and had threatened legal action against Seattle.
It is understood that Martins and Seattle have both contributed to the fee.
- Sports & Recreation