He has been appointed to one of the most senior roles in the Church alongside the president and vice-president of the Conference.
Rev Powell takes over from Rev Dr Martyn Atkins, who said: "I congratulate Gareth in this nomination to be the next secretary of the Conference.
"He is a person of great gifts and I look forward to the next nine months when we shall work together in a time of transition seeking the health, unity of benefit of the whole Methodist Church."
Rev Powell has been assistant secretary of the Conference since 2011 and is currently head of governance support in the Connexional Team.
From 2002 until 2008 he was Methodist chaplain and chaplaincy coordinator at Cardiff University.
He said: "Martyn has helped to create in the Church a fresh enthusiasm for God's calling on Methodists to engage joyfully and seriously with mission and evangelism.
"My commitment to this vision means that I want the Church to pay careful and considered attention to its patterns of oversight and pastoral care.
"In doing so, I hope we will be better resourced and enabled to respond to the challenges of the gospel and of contemporary society."