The German manager took his place on the sidelines at a sold-out Camp Nou despite his personal tragedy, steering his side to a result that put Barca out of reach of their rivals with three matches to play.
Before kickoff, the stadium observed a minute's silence in tribute. Broadcast images showed Flick in tears, comforted by members of his technical staff and players in a poignant moment that set an emotionally charged tone for the evening.
On the pitch, Barcelona delivered the flourish to a campaign built on momentum, nerve and an unwavering commitment to attack, cementing Flick's bond with a demanding fan base who have embraced his bold and aggressive approach.
"It was a tough match, and I'll never forget this day," an emotional Flick said to a packed Camp Nou during the title celebrations.
"I want to thank the squad and all the people who have supported us. The most important thing is that I'm very proud to have such a good team. Thank you for everything."
The typically reserved manager kept his victory address concise amid the festivities, adding: "Thank you for that determination to fight in every match. I really appreciate it.
"My team is fantastic, and I'm delighted. I'm so proud of my players. It's thrilling to be here with the fans, in a Clasico, beating Real Madrid. Now I think we need to celebrate."
The title caps a remarkable campaign for Flick, whose occasionally hair-raising but rarely dull tactical approach has proven both consistently entertaining and ultimately successful in Spain's top flight.