The former Spain and Barca midfielder saw his players secure the trophy with a 3-0 win over Umm Salal that puts them 13 points clear with four rounds of games remaining.
Xavi previously helped Al Sadd land the 2018-19 title in what proved to be the final year of his playing career.
The 41-year-old stepped up to be head coach of the team following that campaign and has led Al Sadd to a string of trophy successes in cup competitions, but he was thrilled to finally land a league title.
"We created a new history for Al Sadd," Xavi said. "I am happy to win the league title for the first time as a coach with Al Sadd, after winning it as a player."
Goals from Baghdad Bounedjah, Yousuf Abdurisag and Rodrigo Tabata secured Sunday's win.
Xavi told the club's website: "I am happy to be in this group of players, officials, technical and medical staff. Our goal is to win all the tournaments we participate in.
"Special thanks to the fans of Al Sadd who supported the team with full force throughout the season and also in the championship match against Umm Salal, and we promise them to continue working to make them happy and win more championships for the club."
Those supporters will hope Xavi's message signals a long-term commitment to the Al Sadd cause, given he has frequently been linked with a return to LaLiga giants Barcelona, the club where he spent his entire career until moving to Qatar at the age of 35.
Such suggestions were revived during the campaign to decide Barcelona's new president; however, the man heading for victory in the vote on Sunday, Joan Laporta, indicated recently that Xavi may not yet have sufficient experience to return to Camp Nou as head coach.
Al Sadd's league title was the 15th in their history and a 75th trophy in total, the club said.