The former England captain signed off from the American club with a 3-1 victory against Houston Dynamo, and broke down in tears after receiving a standing ovation from fans
The Los Angeles side clinched the championship with Robbie Keane scoring a penalty in the 92nd minute to confirm the victory, after which Beckham was substituted to a standing ovation.
And the former Manchester United and Real Madrid midfielder described the success as an "emotional" one to rank alongside his past achievements - but the 37-year-old has no intentions of retiring just yet.
"It's a dream ending," he told Sky Sports News.
"I didn't want to speak about it before the game because I didn't want to jinx it. But it doesn't get much better than this.
He continued: "My last year at Manchester United I won the championship, my last year at Real Madrid I won the championship and my last year playing with the Galaxy I won the championship.
"It's emotional. I have got my family here, my friends here, people that have worked with me for the last six years over here, the backroom staff at the Galaxy, the fans - everyone involved at this club has been exceptional."
The former England captain departed to chants of "Thank you Beckham" from the crowd and broke down in tears after the final whistle, describing it as a "sad, special day."
"It's special to get any victory in a cup final, in front of our home fans," he told ESPN. "It's an amazing day today. I'm sad it's the end - it's been a special place for me and it will continue to be a special place for me."
Beckham did not reveal which club he would be playing for next, but refused to rule out a return to the MLS in the future - and will stay committed to building support for the league: "I have no idea [where I will be playing] I'm happy that I'm wearing this uniform today and that I have been part of this club for six years. I'm very thankful for that."
"I'm going to continue my commitment to this league and this country and my commitment will be the same as it was when I first came here six years ago.
"I might not be playing here anymore but my commitment stays the same to growing this league and growing this sport," he added.