In 1900, Hearts agreed Rennie's transfer to Celtic, however a problem with his contract ensured he never officially joined the Glasgow club. Instead, he signed for Hearts' city rivals Hibernian, where he became an important figure in one of the most successful eras in the club's history. He helped them to claim the 1901-02 Scottish Cup, defeating Celtic 1–0 in the final, with contemporary match reports crediting him with several notable saves. Hibs triumphed despite the final being played at Celtic Park, the home ground of their opponents, as a result of Ibrox's unavailability following the partial terracing collapse which occurred during the annual Scotland v England match two weeks earlier. The following year, Rennie helped Hibs to their first ever League title. Rennie and captain Bobby Atherton were the only two players to appear in every match during that campaign.