Thousands of people protesting the change gathered in pouring rain outside parliament, where members of the lower house voted to approve a set of bills backed by Prime Minister Shinzo Abe
Opposition parties boycotted the vote. The bills will now move to the upper house of parliament, where Abe's coalition holds a majority.
The Prime Minister has been trying to make Japan, a key U.S. ally, more assertive militarily. Last year, he sanctioned a reinterpretation of the country's pacifist post-World War II
constitution, drawing widespread protests.
The bills going through parliament at the moment will allow the Japanese military, known as the Self-Defense Forces, to join its allies in a limited role in conflicts abroad.
U.S. welcomes change
The United States has supported Abe's push.
"We certainly welcome, as we've said before, Japan's ongoing efforts to strengthen the alliance and to play a more active role in regional and international security activities," U.S. State Department spokesman John Kirby said Wednesday.
In April, the two countries announced significant changes
to the guidelines that govern their defense relationship, saying Japan would be able to defend allies that come under attack.
Japanese troops operating overseas had previously been limited to humanitarian roles.
Beheadings by ISIS
But many Japanese people are fearful of the consequences of taking a tougher military stance, worrying it could draw Japan into wars by allies and put soldiers and citizens at risk.
The country was shaken this year by the beheadings of two of its citizens by ISIS
, which linked the killings to the Japanese government's pledge to provide funds to help people affected by the terrorist group.
The security bills have drawn criticism from high-profile figures, including the renowned animator and director Hayao Miyazaki
Opposition lawmaker Yukihisa Fujita told CNN this week that the change will "damage the way Japanese people and country is viewed. It will damage the view of Japanese as a diplomatic nation."
China and South Korea have also expressed concern about Japan's shifting military stance.