The 24-year-old from Runcorn became Britain's first champion in the event's 17-year history when she won in 2016.
Coxsey needed to finish ninth or higher to guarantee back-to-back titles, but took gold in the penultimate event of the season in Mumbai.
Japan's Miho Nonaka finished second, with compatriot Akiyo Noguchi third.
Sport climbing - which includes bouldering - is one of five new sports confirmed for the 2020 Tokyo Olympics.
Britain's Shauna Coxsey won a second successive Bouldering World Cup overall title after victory at the Navi Mumbai event in India on Sunday.