
The southerners finished fifth, one point behind fourth-placed Juventus, after a 1-1 draw at home against Hellas Verona.
A win would have guaranteed a top four finish, but Napoli miss out on a second season of Champions League football.
“Dear Rino, I am happy to have spent almost two seasons with you,” De Laurentiis wrote on Twitter.
“Thanking you for your work, I wish you success wherever you go. A hug to your wife and children too. Aurelio De Laurentiis.”
The relationship between the pair had been tense with the club having imposed a media boycott for months.
Former AC Milan coach Gattuso took over after Carlo Ancelotti was sacked in December 2019.
The 43-year-old also missed out on a Champions League return with AC Milan in the 2018-2019 season by just one point.
The Italian 2006 World Cup winner as a player has been linked with clubs including Fiorentina and Tottenham.