SEOUL—South Korea’s president lifted his martial-law declaration after Parliament voted against the measure, rejecting his claim that political opponents had made the nation vulnerable to North Korean “communist forces.” President Yoon Suk Yeol’s address at around 4:30 a.m. local time on Wednesday ended what had been a tense night sparked by his earlier announcement. Martial law had been declared more than two hours earlier, taking effect at 11 p.m. local time on Tuesday.