In Friday's party vote, Mr. Kan defeated Shinji Tarutoko, a relatively unknown legislator backed by the party's shadowy power broker, Ichiro Ozawa. Kan won with 291 votes to Tarutoko's 129.
Kan, known for being a short-tempered yet proactive politician, first came to prominence in the 1990s when as health minister in an era of closed-door politics and backroom dealings by the "old guard," he exposed a government cover-up of HIV-tainted blood products that caused thousands of hemophilia patients to contract the virus that causes AIDS.
Japan's new leader was first exposed to politics in his younger years as an activist involved in a number of civic movements.
He lost three elections before winning his first seat in the lower house in 1980 for the now-defunct United Social Democratic Party (USDP) with a "civil guerrilla" grass roots environmental campaign.
The DPJ will be counting on Kan to win back the trust of the public and analysts suggest the veteran politician's history of battling Japan's powerful bureaucrats, past civil rights activities and short fuse, will make for a more powerful, resolute and decisive leader, in comparison to his predecessor.
Related:
Uphill battle for Japan's new leader to put Hatoyama's wrongs to right
Naoto Kan becomes DPJ chief, prime minister post certain
