Japanese Prime Minister Fumio Kishida's ruling LDP defied expectations and held on to a stable majority in Sunday's parliamentary election, solidifying his position in a fractious party and allowing him to ramp up stimulus.

Kishida's conservative Liberal Democratic Party (LDP) emerged with fewer seats in the powerful Lower House than it won in the last election in 2017. But the LDP maintained its single-party majority in a big victory for Kishida, who took power only a month ago...