The deal will keep the World Cup star at Al Sadd for three years.
The contract was signed at the club headquarters in the presence of General Manager Turki Nasser Al Ali and Mohamed Ghulam Balooshi, the Al Sadd Sports Director.
The 28-year-old Korean appeared at the 2018 FIFA World Cup in Russia where the Asian champions were eliminated in the first round. Woo-young played for Korea when they beat 2014 World Cup winners Germany 2-0.
The signing of Woo-young comes days after the captain of Atletico Madrid Spanish player Gabi Fernandez signed a two-year spell with Al Sadd. Fernandez will join compatriot and Barca legend Xavi Hernandez at Al Sadd.
The players will join the team's departure on Thursday for Austria for a pre-season training camp which will end on July 28.
Al Sadd - coached by Jesualdo Ferreira - will play four friendlies during their pre-season training camp.
Al Sadd face Al Kharaitiyat in their first round match in the QNB Stars League at the Khalifa International Stadium on 5 August.
Source: qsl.com.qa