Andy Savage, a leader of Highpoint Church in Memphis Tennessee, admitted involvement in inappropriate behaviour with Jules Woodson, after she detailed the incident in her blog last December.
Posted on the church's website, his official statement reads: "As a college student on staff at a church in Texas more than 20 years ago, I regretfully had a sexual incident with a female high school senior in the church.
"I apologized and sought forgiveness from her, her parents, her discipleship group, the church staff, and the church leadership, who informed the congregation."
He said he "took every step to respond in a biblical way" and resigned from ministry.
He added that he "accepted full responsibility" for his actions and "was and remain very remorseful for the incident and deeply regret the pain I caused her and her family, as well as the pain I caused the church and God's Kingdom".
Lead pastor Chris Conlee also responded to the sexual assault in a statement below Savage's on the church's website.
He said: "This information is not new to me or to our leadership.
"As one of my closest friends and partners in ministry, I can assure you that I have total confidence in the redemptive process Andy went through under his leadership in Texas.
"On behalf of the elders, pastors, staff, and Trustees of Highpoint, I want to affirm that we are 100 per cent committed to Andy, Amanda, and their family and his continued ministry at Highpoint Church.
"We ask for your prayers and support for all involved."
