Martinez has been available as a free agent in recent weeks, following his exit from Bayern Munich, with the Bavarians opting against giving either him or David Alaba a contract extension.
The 32-year-old was initially linked with a fairy tale return to the Estadio San Mames with the Basque giants open to a short term deal for the experienced No.6.
However, he has now opted against a return to Spain, and will join up with his new club ahead of the start of the Qatari Stars League in September.
— Qatar SC (@QatarSportClub) June 20, 2021
Martinez made 251 appearances with Athletic Bilbao between 2006 and 2012 before moving on to Bayern in a high profile €30m deal.
He played a key role in Bayern’s Bundesliga dominance during nine seasons at the Allianz Arena, with nine consecutive league titles and two Champions League winners medals.