In an acceptance speech, Kishida vowed to lead a transformed party in a general election due within weeks and continue to fight the COVID-19 pandemic which has battered Japan's economy.
"From today, I will, with all of my energy, get straight to work. Party members around the country and members of the parliament, please work with me," he said.
However, Kishida enjoys only moderate public support and has a bland image and his victory could spell problems for the LDP in the election due by Nov. 28.
Kishida defeated former defense and foreign minister Taro Kono, seen as an outspoken maverick, in a second round run-off vote.
The winner of the party poll to succeed unpopular Prime Minister Suga, who is not seeking re-election after just one year in office, is almost certain to become premier because of its majority in parliament's lower house.
Kishida's victory is unlikely to trigger a huge shift in policies as Japan seeks to cope with an assertive China and revive an economy hit by the pandemic, with the soft-spoken MP highlighting the need to focus on reducing income disparity.