In a blog on his website the American says "countless hours of prayer, study, conversation and emotional turmoil" have brought him to a place where he's ready to speak up for gay people in the Church.
In a big move away from his previous traditional stance on the issue, he says spending time with same sex couples has allowed him to rethink.
He said: "Our friendships with these couples have helped me understand how important it is for the exclusion and disapproval of their unions by the Christian community to end.
"We in the Church should actively support such families. Furthermore, we should be doing all we can to reach, comfort and include all those precious children of God who have been wrongly led to believe that they are mistakes or just not good enough for God, simply because they are not straight."
He also suggested that the treatment of gay people from those inside the Church is similar to how it previously treated women and slaves.
He said: "I am old enough to remember when we in the Church made strong biblical cases for keeping women out of teaching roles in the Church, and when divorced and remarried people often were excluded from fellowship altogether on the basis of scripture.
"Not long before that, some Christians even made biblical cases supporting slavery. Many of those people were sincere believers, but most of us now agree that they were wrong. I am afraid we are making the same kind of mistake again, which is why I am speaking out."
Also in the blog, he criticises Christians who try to 'cure' gay people.
He finishes by claiming he "could be wrong on this one" but called on all Christians to do more to welcome gay people into the Church.
Listen to Revd Steve Chalke of Oasis and friend of Tony Campolo giving his thoughts to Premier's Marcus Jones on the News Hour:
Listen to Church of England priest and commentator on sexuality Revd Peter Ould giving his thoughts to Premier's Marcus Jones on the News Hour: