She participated in the 1988 Miss Thailand pageant held in Bangkok where she won and had the right to represent Thailand at the Miss Universe pageant.
At age of 19, Porntip Nakhirunkanok was crowned as Miss Universe 1988 by outgoing titleholder Cecilia Bolocco on May 24, 1988 in Taipei, Taiwan. She entered the semi-finals in fourth place, right behind USA, Dominican Republic, and Korea. She impressed the judges so much during the interview portion that she swept the competition, becoming the clear winner for the evening. She received the interview score of 9.730, swimsuit score of 9.684 and 9.752 for evening gown respectively.
The 1988 pageant is notable for the fact that four of the top 5 finalists all hailed from the Far East, with Porntip as the winner, Korea (Yunchung Chong) in second, Mexico (Amanda Olivares) in third, Japan (Mizuho Sakaguchi) in fourth, and Hong Kong (Pauline Yeung Bo Ling) in fifth. The rest of the top 10 were Patricia Jimenez from the Dominican Republic, Yajaira Vera-Roldán of Venezuela, Courtney Gibbs of USA, Diana Patricia Arévalo of Colombia, and Bente Brunland of Norway.