The group of 111 pastors, deacons, elders and candidates for ministry posted a public letter about their sexuality online.
Church rules demand "that we not bring our full selves to ministry, that we hide from view our sexual orientations and gender identities," they said.
The letter, which was seen by CNN, states that some of them have been "lucky to serve in places where we could serve honestly and openly".
It adds: "There are others in places far more hostile, who continue to serve faithfully even at tremendous cost to themselves, their families, and yes, even the communities they serve, who do not receive the fullness of their pastor's gifts because a core part must remain hidden," the letter continues.
The declaration was published as the General Conference of the Church begins in Portland.
Some of the delegates will try and raise a bill to change Church policy on LGBT (lesbian, gay, bisexual and transgender) ministers and same-sex marriages.
The group warn that if they rules are not changed they would be willing to walk away from the Church, one of the largest protestant denominations in the US.
"Even if we should leave and you seek more restrictive language against LGBTQI persons, know that God will continue to move mysteriously in the hearts of LGBTQI young people and adults and will call them to serve within this denomination," they say. "You cannot legislate against God's call."
The group say they are coming out as gay "to provide hope for LGBTQI young people in hostile UMC churches".
The letter comes just weeks after a bishop at the church performed a same-sex marriage for two men in North Carolina.
The United Methodist Church rules state that the "practice of homosexuality" as "incompatible with Christian teaching."
All of those who have signed the letter now face disciplinary action and could even be removed from ministry.
Hillary Clinton and George W. Bush are among the seven million members of the church.