In a letter read to the congregation of the conservative New Life Church by another clergyman, Mr Haggard apologised for his acts and requested forgiveness.
"I am so sorry for the circumstances that have caused shame and embarrassment for all of you," he said, adding that he had confused the situation by giving inconsistent remarks to reporters denying the scandal.
"The fact is I am guilty of sexual immorality. And I take responsibility for the entire problem. I am a deceiver and a liar. There's a part of my life that is so repulsive and dark that I have been warring against it for all of my adult life," he said.
Mr Haggard resigned last week as president of the National Association of Evangelicals, where he held sway in Washington and condemned homosexuality, after a male prostitute claimed to have had drug-fuelled homosexual trysts with him.
Mr Haggard also placed himself on administrative leave from the New Life Church, which has
14,000 members, but its independent Overseer Board fired him yesterday.
In his letter, Mr Haggard said "the accusations made against me are not all true but enough of them are that I was appropriately removed from his church leadership position."
He did not give details on which accusations were true.
The letter was read to the church by the Reverend Larry Stockstill, senior pastor of Bethany World Prayer Centre in Baker, Louisiana, and a member of the board that fired Mr Haggard.
Church crisis
Before the letter was read, members of the congregation sang and cheered during the Sunday service, singing refrain after refrain of "I will bless the Lord at all times."
Youngsters were sent out of the room before elders began speaking about the church crisis.
"Worshippers are always challenged by crisis. And when tragedy and crisis strikes, it is at that moment that you truly decide if you are a worshipper of the most high god. And today, as the worship pastor of this church, I am very proud of you," said the Reverend Ross Parsley, who has replaced Mr Haggard.
"I am so grateful for the government system in place here at this church. ... The speed with which things were dealt with this week has been a testimony to the godliness, to the integrity and authority of the overseers of the board of this church," he said.
Mr Haggard, 50, had acknowledged on Friday that he paid Mike Jones of Denver for a massage and for methamphetamine, but said he did not have sex with him and did not take the drug.
The Overseer Board, made up clergy from various churches, used stronger language.
"Our investigation and Pastor Haggard's public statements have proven without a doubt that he has committed sexually immoral conduct," the board said in a statement.
The NEA, representing 30 million evangelicals, named the Reverend Leith Anderson, senior pastor of Wooddale Church in Eden Prairie, Minnesota, as its interim president.
Mr Haggard's situation is a disappointment to Christian conservatives, whom President George W Bush and other Republicans are courting heavily in the run-up to Tuesday's election.
Mr Haggard, who had been president of the evangelical association since 2003, has participated in conference calls with White House staffers and lobbied Congress last year on Supreme Court nominees.
Mr Haggard founded New Life in the mid-1980s and held its first services in the basement of his Colorado Springs home.