The company also noted new records for passengers and their cars - both figures advanced by 2.5% year-on-year to 1.5m and 360k, respectively.
Stena Line offers three services from its hub in Belfast - to Cairnryan, Liverpool, and Heysham. These routes are served by seven vessels, which altogether offer 22 daily sailings.
"Whilst Stena Line has delivered a record performance in 2017, we will continue to focus on providing even higher levels of customer service in 2018 which is why we will be investing a further £500k in the upgrade of our onboard passenger facilities this spring," Paul Grant, Stena Line's Trade Director (Irish Sea North), commented.
He also said, "Belfast Harbour's on-going success is supported by another record year for Stena Line. We have been partners for more than 20 years and have seen their business here grow significantly during that time. 2017 is no different with increases in passengers, freight, cars and coaches. This is down to their vision and hard work as well as adapting to the market and we look forward to continuing to support them and the growth of their business in the coming years."