The move by bishops will allow Anglican churches in the US to use new liturgy to marry same sex couples, however no priest will be forced to perform the ceremonies.
The US Episcopal Church has seen big divisions over issues of gender and sexuality and in recent years they have led to a split and the formation of the new Anglican Church in North America.
Most Revd Justin Welby is currently overseeing on-going conversations on the issues of sexuality and marriage within the Church of England in light of the government's decision to legalise same sex marriage in 2014.
In response to the change in the US, a statement from Lambeth Palace said: "While recognising the prerogative of The Episcopal Church to address issues appropriate to its own context, Archbishop Justin Welby said that its decision will cause distress for some and have ramifications for the Anglican Communion as a whole, as well as for its ecumenical and interfaith relationships.
"At a time of such suffering around the world, he stated that this was a moment for the church to be looking outwards. We continue to mourn with all those who are grieving loved ones and caring for the injured from the terrorist attacks in Sousse, Kuwait and Lyons, and from the racist attacks in Charleston.
"He urges prayer for the life of the Anglican Communion; for a space for the strengthening of the interdependent relationships between provinces, so that in the face of diversity and disagreement, Anglicans may be a force for peace and seek to respond to the Lord Jesus' prayer that "they may be one so that the world may believe" (John 17: 21)."