David Black's funeral cortège arrived at the Molesworth Presbyterian Church, lead by a lone piper.
The coffin was carried by prison officers and David Black's son Kyle, who will also speak during the service.
There was silence as the coffin was carried into the church for the service. Hundreds are gathered outside with the service being relayed on loud speaker.
Three men, aged 31, 29 and 44, have been arrested following the killing of prison officer David Black in Northern Ireland.
Leaders in Northern Ireland have condemned the "horrific" motorway murder of a veteran prison officer by suspected dissident republicans.