Trains have started running from the new Belfast Grand Central Station.
The first Enterprise train left the station at 8.05am on a journey to Dublin Connolly Station.
The rail line also reopened between Belfast and Lisburn, which had been closed for a period of time.
An hourly Enterprise service between Belfast and Dublin is planned to start on Tuesday October 29.
The £340 million station opened in September with bus services running while works were ongoing for prepare for the rail services.
It is to become the largest integrated transport hub on the island of Ireland, replacing the Europa Bus Centre and the former Great Victoria Street Station.
Welcoming the start of services, Infrastructure Minister John O’Dowd said: “This is another significant step in the development of our public transport offer.
“I am delighted that rail services have started from Grand Central Station.
“The reopening of the rail line between Lisburn and Belfast is good news for the thousands of commuters and cross-border passengers who use this route.
“Belfast Grand Central Station is the largest transport facility on the island of Ireland with the capacity to cater for 20 million passenger journeys a year.
“With right rail platforms and 26 bus stands this new facility demonstrates how infrastructure can transform and make a difference.
“Many people have been working tirelessly to get us to this point today and I thank them all.
“Most of all I would like to thank the public for their patience while we carried out the important rail safety authorisation process which was vital in making today a reality.”
Chris Conway, Translink Group chief executive, said: “The commencement of rail services at Belfast Grand Central is a significant milestone in the transformation of public transport in Northern Ireland, providing integrated services which connect people and place.
“The first Enterprise departure at 8.05am today was a truly historic moment, marking the start of rail services at this iconic new facility and the return of cross-border rail services to the heart of the city.
“With new rail timetables in place and many new features at the station including new ticket gates, we would encourage passengers to plan ahead and build in a bit of extra time for your journey until you familiarise yourself with the new station.
“I would like to thank everyone involved in getting us to this historic milestone and express my thanks to all our passengers, community and stakeholders for your patience throughout this work.”
Tom Newman, chief executive of Babcock’s Land business, said: “We are proud to have supported Translink on the development of Belfast Grand Central Station, playing an important part in ensuring the people of Belfast and its visitors benefit from this world-class transport hub.”
