The 34-year-old opened the scoring from the penalty spot as USA defeated Netherlands 2-0 in Lyon on Sunday to claim back-to-back global titles.
She finished level on six goals with team-mate Alex Morgan and England forward Ellen White but edged the Golden Boot by virtue of a better minutes-per-goal ratio.
It marked Rapinoe's first Golden Boot in her third World Cup appearance and she could not describe the feeling after the match.
"I don't know how to feel right now, it's ridiculous," she said.
— FIFA Women's World Cup (@FIFAWWC) July 7, 2019
Rapinoe started with one goal in the group stage and followed it up with back-to-back braces, scoring all four of USA's goals in the knockout phase before the semi-final, for which she was an unused substitute.
She was also crowned the tournament's best player for her performances, with England's Lucy Bronze taking the Silver Ball and Rose Lavelle, who scored USA's second in the final, claiming third.
Photo Getty Images. Caption: Megan Rapinoe with the World Cup, Golden Boot and Golden Ball trophies