A Taiwanese lawmaker, previously blacklisted by Beijing for alleged pro-independence sentiments, has announced a long-shot candidacy for Taipei mayor. The move comes as a surprise within the ruling party.

A first-term lawmaker who was blacklisted by Beijing over his alleged support for Taiwanese independence will challenge Taipei’s popular incumbent mayor in the local elections later this year. The ruling Democratic Progressive Party’s decision to nominate Puma Shen Pao-yang, an outspoken critic of Beijing whose political identity has been built around his calls to strengthen the island’s security, came as a surprise to many. The former academic joined politics only two years ago, entering the...