Benchers — as board members are known — voted 25-to-one to ratify the vote on Friday morning.
More than 8,000 of the society's 13,530 members voted earlier this month in a special referendum to overturn the board's decision earlier this year to accredit the faith-based law school when it opens in 2016.
Critics oppose the new law school's accreditation because Trinity Western students must sign a Christian covenant that states sexual relations are to be confined within the bounds of a marriage between a man and a woman.
Critics say the policy is discriminatory against people in LGBTQ relationships.
The Law Society of Upper Canada in Ontario has voted against approving the law school and the Nova Scotia Barristers' Society has granted conditional acceptance if the school changes the covenant for law students or allows them to opt out.
Trinity Western is legally challenging those decisions in court, arguing they have a right to religious freedom.