On Saturday, the Presbyterian Church will ordain Scott Anderson, its first openly gay minister.

Anderson's ordination comes after the 2 million member Presbyterian Church (USA) began welcoming non-celibate gay clergy in July. A policy change decades in the making.

In the spring of 1990, Anderson was serving as the head pastor of Bethany Presbyterian in Sacramento, California when he was outed by two parishioners. Soon after, he departed from the church.

“Getting outed at Bethany was both the best and worst moment of my life,” Anderson is quoted as saying at the Christian blog JohnShore.com. “On the one hand, it was so freeing and empowering to finally be honest about the truth of who I am. On the other hand, it forced me to step away from my passion. The gay issue had never been part of my ministry at Bethany; it hadn't played any role at all in our conversations there. When out of the blue it became the conversation, I thought it best if I voluntarily resigned from Bethany. I didn't want the tumult caused by my staying to ultimately prove disruptive in the life of the church.”

Anderson and his partner Ian MacAllister have been together 20 years.

Saturday's ceremony at the Covenant Presbyterian Church in Madison, Wisconsin is expected to be protested by the anti-gay Westboro Baptist Church.

“That's an important event in Heaven and on Earth,” Margie Phelps, daughter of Fred Phelps, who founded the Topeka, Kansas-based church, told WISC-TV. “And it's our duty as the church of the Lord, Jesus Christ, to come to the scene and remind people of their duty to God, so that's why we're coming.”

Other mainline Protestant denominations in the United States have approved the ordination of gay clergy in recent years, including the Episcopal Church, the Evangelical Lutheran Church in America and the United Church of Christ.

The ordination of two gay bishops prompted conservatives to split from the Episcopal Church and form their own church.