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.
The former Barcelona star says he is "feeling okay" but is self-isolating as per competition protocols.
In a statement released via the club's website on Saturday, the Spain great said: "Today I won't be able to join my team on their comeback to the official competition.
"A few days ago, following the QSL protocol, I tested positive in the last COVID-19 test. Fortunately, I'm feeling okay, but I will be isolated until I am given the all-clear.
"When the health services allow it, I will be very eager to return to my daily routine and to work.
"I'd like to thank all the authorities, especially those working in QSL, QFA [Qatar Football Association] and Al Sadd for supplying the means of early detection, reducing the spread of infection and that guarantees the normal development of the competition.
"Take care and see you soon on the football pitch!"
Reserve team coach David Prats will take charge for the match, Al Sadd's first since the league was suspended in May.
The 40-year-old confirmed on Saturday that he had tested positive for COVID-19 and was spending time away from his Qatari club.
It meant he missed out on coaching the team in their Stars League clash with Al Khor, but Xavi is well again, he declared on Instagram.
The former Spain midfielder, who has been frequently linked with a Camp Nou return as a potential successor to head coach Quique Setien, posted pictures of himself both back at work and at home with his children.
In a post published on Wednesday, Xavi thanked followers for their "caring messages" since announcing he had coronavirus, adding: "I want to share with you that I'm recovered and back home with my family and the @alsaddsc team".
In a separate Instagram post, Al Sadd also showed Xavi on club duty, wearing a face mask as he welcomed new signing Rodrigo Tabata to the club.
Barca's first vice-president Rafael Yuste and director of football Mateu Alemany were in attendance for Al Sadd's 3-3 draw with Al Duhail on Wednesday, a result that kept Xavi's side three points clear at the top of the Stars League.
The former midfielder, who made 767 appearances for Barca as a player and won 25 trophies during an illustrious spell for the club, has been the frontrunner to take over following the dismissal of Ronald Koeman last week.
Al Sadd last week insisted Xavi was solely focused on the Qatari club, with whom he has a two-year contract, but the coach confirmed an agreement on his future could be reached in a matter of hours.
"I really want to go home. The two clubs are in talks and a resolution must be reached. I am very excited, but it's a matter of respect – I have a contract," Xavi told Mundo Deportivo.
"It would be a return home. The two clubs have to agree. Hopefully it will be done, because I am very eager and excited.
"I am very positive. I have been very clear about my position. I think it will be a matter of hours, maybe days. They know my stance and hopefully it can be done."
He added to TV3: "I am a positive person and it is a matter of common sense. They have to agree. The two clubs know my position and I hope it will be sorted soon."
After a 1-1 draw with Deportivo Alaves in their first game since Koeman's dismissal, Barca boosted their qualification hopes in the Champions League by beating Dynamo Kiev on Tuesday.
Speaking more generally about what Koeman's successor needs to do at Camp Nou, Xavi added: "The coach who goes does not have to be a messiah. We saw a different Barca yesterday.
"Everyone has to row in the same direction for Barca to win games. We are all very excited. We will see if it ends up being done, but it would be spectacular."
A Barca great, Xavi has long been tipped to return to Camp Nou as head coach – firstly before Ronald Koeman's appointment at the start of 2020-21 and after Joan Laporta's presidential election victory.
But Spaniard Xavi will remain in charge of Qatari side Al-Sadd until 2023, it was announced on Wednesday.
The 41-year-old has guided Al-Sadd to Qatar Stars League (2020-21), Qatar Cup (2020 and 2021), Qatari super Cup (2019), Emir of Qatar Cup (2020) and Qatari Stars Cup (2019) success since becoming coach in 2019.
"We achieved a lot together, scored goals, won matches and titles, and we are all very proud of this success. Getting this kind of support is the best thing any coach can get," said Xavi, who spent 17 years with Barca, where he won eight LaLiga trophies and four Champions League titles among other honours.
"I have everything I could want to do well, and I feel proud to continue with Al-Sadd for an additional two seasons."
Xavi – who held the record for most Barca appearances before it was broken by Lionel Messi this season – also denied he has a clause in his contract that allows him to leave Al-Sadd amid Barca links.
"This is incorrect," the former Spain international added. "I have a two-season contract with Al-Sadd, and I respect this contract - and I also respect the official negotiation methods between all parties."
Barca icon Xavi confirmed on Thursday that he had declined the opportunity to succeed Ernesto Valverde at Camp Nou.
Valverde was sacked on Monday, with former Real Betis and Las Palmas coach Quique Setien swiftly appointed.
Xavi claimed he turned Barca down because he believed it was "too soon" in his coaching career to take such a job, yet he will have done his credentials no harm with Friday's triumph.
Nam Tae-hee opened the scoring early on for Al Sadd, with Baghdad Bounedjah then doubling their tally after a mistake from Duhail's goalkeeper Amine Lecomte.
Bounedjah helped himself to a second before half-time, with Akram Afif's penalty completing the rout midway through the second half.
Friday's victory secured Xavi his second piece of silverware in charge of Al Sadd, who won the Qatari Super Cup in August last year.
Barca, meanwhile, kick-off the Setien era with a home match against Granada in LaLiga on Sunday.
Al-Sadd boss Xavi was linked with the Barca vacancy earlier this year when the LaLiga champions sacked Ernesto Valverde, before they turned to Quique Setien in January.
Barca have struggled to convince this season – the titleholders now two points behind bitter rivals Real Madrid in the race for LaLiga glory with six matches remaining.
While outlining his future plans for Barca, the 40-year-old insisted he will not come back unless he has the control to make decisions.
"The biggest hope I have now is to be Barca coach and get Barca back to winning ways," Xavi, who has led Al-Sadd to Qatari Super Cup and Qatar Cup silverware, said via Sport.
"Not me but these players and Barca triumphing. And as a consequence, our technical staff, who are preparing for it a lot and it makes us really excited."
Xavi, who won 25 trophies during his playing career with Barca, added: "I'm a club man. I would like to return at the right moment to start a project from zero.
"I've said it a lot of times but I want to take footballing decisions at Barcelona.
"It's clear that after the elections the stage would be set, of course. I'm not ruling anything out.
"They came for me in January, we were speaking. I told them the circumstances and timing weren't right."
