Odegaard joined Madrid in 2015 but has spent the past two and a half seasons out on loan in the Eredivisie, with Heerenveen and Vitesse respectively.
Official Announcement: Odegaard.#RealMadrid— Real Madrid C.F. 🇬🇧🇺🇸 (@realmadriden) July 5, 2019
His spell at Vitesse last season proved fruitful as the attacking midfielder scored 11 goals from 39 appearances in all competitions.
However, the 20-year-old has not been considered ready to compete for a place in Madrid's first team, with Los Blancos sending Odegaard out on loan for a fourth successive campaign.
OFFICIAL ANNOUNCEMENT: Real Sociedad have reached an agreement with @realmadriden over the transfer of @martinio98. The player will join the club on a one-year loan. #OngiEtorriOdegaard #AurreraReala #RealSociedad 💙⚪⬇ pic.twitter.com/4zF2hAvRH3— Real Sociedad (@RealSociedadEN) July 5, 2019
The Norway international has only made one previous LaLiga appearance - coming on as a substitute in Madrid's 7-3 win over Getafe in May 2015 - and will now have the chance to experience Spain's top flight with Sociedad, who finished ninth last season.
Odegaard's move represents a second departure from Madrid to be announced on Friday, with full-back Sergio Reguilon having left for Sevilla on a season-long loan.