In January 1999, Mrmić won his only international cap for Croatia B in a friendly match against France B. He also continued to be Croatia's second-choice goalkeeper during the UEFA Euro 2000 qualifying. His only appearance in the qualifying came in a 2–1 win at home to Malta on 21 August 1999. It eventually turned out to be his final international appearance, as he retired from international football two months later, following Croatia's failure to qualify for the finals.