Veteran striker Giroud put Milan two ahead in the 27th minute at the San Siro, shortly after Rafael Leao had opened the scoring. Giroud welled up after he netted for the 17th time this season.
He will finish his club career at Los Angeles FC after playing his final matches for France at Euro 2024, and he signed off after three eventful years with his 49th goal for the club.
The 37-year-old leaves as a big fan favourite and will be remembered in particular for scoring key goals in Milan's 2022 Serie A triumph, the only trophy he won in his three years in Italy.
When he was substituted with five minutes remaining and Milan still leading 3-1, fans belted out a chant in honour of his winning double in a derby victory which was crucial to their team pipping local rivals Inter Milan to that Scudetto.
Giroud struggled to hold back the tears when speaking to fans on the pitch on an evening of goodbyes.
He called the title win "one of the best feelings of my career" before sharing a touching embrace with his parents.
Simon Kjaer, another Scudetto winner leaving Milan, was equally emotional, telling fans that "the way I feel playing here is the same way I feel playing for my country".
'A fire in my heart'
Pioli, the architect of the league triumph two years ago, was given a warm round of applause by fans and his players, who hoisted him on their shoulders at the end.
"We won and lost together, shared joy and pain together," said Pioli. "You lit a fire in my heart that will not be extinguished. I won't forget you,"
Milan announced on Friday that Pioli would be leaving at the end of the season after an eventful four-and-a-half years in charge which have brought the club back to the upper echelons of Italian and European football.
In addition to the Scudetto he also guided Milan to last season's Champions League semi-finals -- the first time they had gone that far since winning the competition in 2007.
Pioli's fate was sealed by his team's failure to mount a serious challenge as Inter romped to the title, by six straight Milan derby defeats and by an early exit from the Champions League, followed by going out of the Europa League to Serie A rivals Roma.
Pioli, who was under contract until the end of next season, is reportedly set to be replaced by Lille coach Paulo Fonseca.
Juve eye Motta
Juventus are heading towards the Thiago Motta era after finishing their season with a straightforward 2-0 win over Monza.
Goals from Federico Chiesa and Alex Sandro in two first-half minutes were enough for Juve to win just their third league match since the end of January.
Juve, guided by caretaker manager Paolo Montero since Massimiliano Allegri was sacked last week, ended their season by snapping a run of six straight Serie A draws.
Motta is hotly-tipped to become the next Juve boss after the former Italy midfielder decided not to renew his contract at Bologna, who lost at Genoa on Friday.
That defeat for Bologna and Saturday's win allowed Juve to move third, although their final position will depend on how Europa League winners Atalanta do against Torino on Sunday and in their game in hand with Fiorentina next weekend.
Atalanta, five points behind Juve in fifth, have to win their final two games to leapfrog Juve and match their highest ever placing in Italy's top flight.
