Keating spoke of how close the band members all were.
"We will carry on but it will never be the same without him. Forever young and never forgotten. A man, a friend, a brother, a son a husband and a hero. I'm gonna really miss you brother. We love you and always will. And we know you have found peace. Perfect peace."
Mikey Graham spoke of Gately's devotion to his partner Andrew Cowles and of how much he loved his parents Margaret and Martin.
"With an audience, Stephen came alive - he truly became himself," Graham said.
"The band feels black and white without him. We were very lucky to be invited in to see a glimpse of the warm, honest and gentle loving man that he was."
Keith Duffy described Gately as "a giant of a man in our hearts. So many owe him so much for what he did. We were always there for each other through thick and thin."
The crowds threw white roses on Gately's coffin as it left for a private cremation at Glasnevin Cemetery ahead of a funeral party for 450 guests at a hotel in the city.
Boyzone's manager Louis Walsh spoke to journalists before the funeral service.
"He (Stephen) would not believe the reception he's got today. He was living his dream," Walsh said.
Jason Donovan looks at a tribute to Gately outside the church
"It's a fantastic feeling here today - we have to celebrate his life, he would absolutely love what was happening here today.
"He was always professional, he was so likeable. I wouldn't be where I was today if it wasn't for Boyzone. We're all in this together."
The X Factor judge will miss the ITV1 show this weekend because of the funeral.
Former Irish taoiseach Bertie Ahern, members of Boyzone and Westlife, Jason Donovan and Shayne Ward were among the mourners, joining many of Gately's close family and friends.
Fans from as far afield as Taiwan were among the crowds, with many of them laying flowers outside the church.
The remaining members of Boyzone stayed with Gately's body in the church the night before the funeral - singer Keating came out to thank fans for their support in the early hours of the morning before going back inside.
"They brought a bottle of wine in, they cried, they laughed, they cried, they are a very close bunch of mates," said Boyzone backing musician James McNally.
Gately was found dead on a sofa in his Majorcan home, aged 33
Messages of condolences were received from George Michael, David and Victoria Beckham, Simon Cowell, Take That, Westlife, U2, Robbie Williams, Cheryl Cole, Colin Farrell, Sharon Osborne, Brian McFadden and Delta Goodrem.
David Furnish arrived at the church and explained his partner Elton John was in Zurich on tour and could not break his contractual commitments but "was very much there there in spirit".
Loudspeakers relayed the ceremony to well-wishers outside.
Instead of flowers, mourners were asked to make donations to the Caudwell Children Charity, for which Gately was an ambassador.
His grief-stricken bandmates escorted the late singer's body back to his hometown on Friday.
Gately grew up in Dublin but had spent the last few years living in Highgate, London.
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