The company was incorporated on 26 June 1846 with the first section of line from Belfast to Holywood opening for traffic on 2 August 1848.

Thanks to the triangular layout, trains were still capable of operating directly from the main Downpatrick station to Belfast or Newcastle.

[5] The BHBR did not exercise this power, but several years after it had been taken over by the BCDR, the latter company started running scheduled passenger steamship services on the route.

The BCDR took advice from the Glasgow & South Western Railway (G&SWR),[5] which had been running passenger paddle steamers since 1891.

For the 1893 season the G&SWR had ordered a new ship, PS Minerva (1893), to be built by J&G Thomson at Clydebank.

Thomson's launched Slieve Donard on 20 May 1893 and she entered service between Belfast's Donegall Quay and Bangor on 20 June.

[5] Donard and Bearnagh worked between Donegall Quay and Bangor, between them providing six sailings per day from Mondays to Saturdays and five on Sundays.

[7] Bangor Castle had been on charter to the Southampton, Isle of Wight and South of England Royal Mail Steam Packet Company since 1888 and was scrapped in 1899.

Slieve Bearnagh remained with the B&CDR, occasionally making excursions to Portaferry on the Ards Peninsula, Ardglass in south Down, and Larne and Portrush on the coast of County Antrim[5] in addition to her regular scheduled route on Belfast Lough.

At the end of the 1911 summer season the BCDR put Slieve Bearnagh up for sale and ordered a new paddle steamer, again slightly larger than her predecessors.

A & J Inglis of Pointhouse, Glasgow launched the new ship, PS Erin's Isle, on 12 June 1912 and fitted her out in less than a month.

[6] On 19 June 1912 the railway sold Slieve Bearnagh to D&J Nicol of Dundee for service on the east coast of Scotland.

[5] Erin's Isle was in BCDR service from 12 July 1912 until her fourth summer season ended on 29 September 1915.

[11] The line between Castlewellan and Newcastle remained open until 1 May 1955,[13] served by Great Northern Railway Board trains to and from Banbridge.

The railway holds a vast collection of BCDR rolling stock and museum artefacts, the majority of which are on display for the public to enjoy.