[3] Merivienti Oy (English: Sea Export Ltd.) was founded on 18 April 1947 by the Finnish forest industry giant Enso-Gutzeit and Kansaneläkelaitos (Finnish Social Insurance)—both completely or partially state-owned companies—to ensure transportation of forest industry products from Finland to Western Bloc countries.

During the same year, Merivienti decided to start liner traffic from Finland to the east coast of the United States.

[3] In subsequent years, vessels owned by other companies, such as Enso-Gutzeit (for whom they managed SS Enso), Neste, Outokumpu, Yhtyneet Paperitehtaat, Amer-Tupakka and Thomesto.

[6] The company first begun carrying passengers in 1962, when the car ferry MS Hansa Express opened a new service linking Hanko, Finland to Travemünde, Germany via Visby in Sweden.

[6] The ship was found to be too small from the start, and Hanko a poor choice for the Finnish terminus of the line.

[10] In the same year Finnlines also placed an order at the Wärtsilä Helsinki shipyard for a new gas turbine-powered ferry for the Finland-Germany service that was to be the largest, longest, and fastest in the world.

With her 31-knot top speed the Finnjet was able to cross the Baltic in a mere 22 hours, and her accommodations were superior to those of any ferry of the day.

In May 1981 she was sold to the Loke Shipping Co.[12] In October of the same year, the Finnjet was rebuilt with additional diesel engines, allowing for more economic operations during the off-season.

In place of dividends, shares of Finncarriers were given to stock owners, and after several mergers, diffusions, and name-changes, a new Finnlines Group was born in 1990.

[6] Around the same time Finnlines started collaboration with the German shipping company Poseidon Schiffahrt on Helsinki–Travemünde traffic, which was marketed under the name Finncarriers-Poseidon.

During 1994 and 1995 four new combi-roro ships (known as the Hansa class), capable of carrying 114 passengers alongside their freight capacity, were delivered for Finncarriers-Poseidon traffic.

[6] In 2004, Finnlines decided to further simplify the myriad of names under which it operated ships, merging Finnlink and Nordö-Link into the parent company.

[16][17] In January 2007, the Italian Grimaldi Group became the largest owner of Finnlines and expressed interest in purchasing the entire company.

However, a public tender offer made to the other owners in November 2006 resulted in Grimaldi gaining only 85,029 stocks, or 0.18% of the total.

[20] In January 2020, two new ro-pax vessels, named the Superstar class and to be Finnlines' largest ships upon their entry into service in 2023, were ordered from the China Merchants Jinling Shipyard.

[21] Finnlines' roro cargo ships serve Finland, Russia, Sweden, Poland, Germany, Denmark, the Netherlands, Belgium, the United Kingdom, and Spain.