"Un-Break My Heart" attained commercial success worldwide. In the United States, the song reached number one on the Billboard Hot 100, where it stayed a total of eleven weeks, while reaching the same position on the Hot Dance Club Songs and Adult Contemporary component charts. When Billboard celebrated their 40 years charting from 1958 to 1998, the song was declared as the most successful song by a solo artist in the Billboard Hot 100 history. In Europe, the song reached the top five in more than ten countries while peaking at number one in Austria, Belgium (Wallonia), Sweden, and Switzerland.
Bille Woodruff directed the accompanying video for the single. It portrays Braxton mourning the death of her lover, while remembering the good times they had together. Braxton performed the song on the opening ceremony of the 1997 Billboard Music Awards.