|Shipyard:||Wärtsilä Shipyard, Turku, Finland|
|Launched:||28 September, 1984|
|Delivered:||17 May, 1985|
|Current route:||Stockholm — Mariehamn — Helsinki|
|Propulsion:|| 4 × Wärtsilä-Pielstick diesels|
|Ice class:||1 A Super|
|Sister ship:||MS Pride of Bilbao|
MS Mariella is a cruiseferry delivered in 1985 to SF Line and has since operated as a part of Viking Line. She was built by the Wärtsilä Shipyard in Turku, Finland. Her sister ship is the Olympia (now Pride of Bilbao).
When the Mariella was delivered in 1985, she was the first ship on Viking Line's Helsinki—Stockholm service which was not owned by Rederi Ab Sally. She has remained on the same route ever since, except for a few brief times when she has been moved temporarily on to other Viking Line routes. This makes her the record holder for the longest continual service on the Helsinki—Stockholm route. At the time of her delivery, the Mariella was the largest ferry in the world in terms of gross tonnage, number of passengers and passenger berths.
In 1989, ahead of the delivery of the new MS Cinderella, SF Line considered moving Mariella on to a proposed express Helsinki—Norrköping service aimed at passengers travelling with their cars. The plan never materialised, and Mariella continued to serve on the same route even after the Cinderella was delivered and placed as the third ship on the route. Following the bankruptcy of Rederi AB Slite in 1993, SF Line was left as the sole operator of the Viking Line name, but this had no effect on Mariella's traffic.
Mariella was the first ship to arrive at the scene of perished MS Estonia in September 1994. 15 survivors were picked up from the sea and another eleven were brought onboard by helicopters, as Mariella was used as the main helicopter platform.
During the 1996 summer season a short cruise from Helsinki to Tallinn was added to Mariella's schedule in place of the nine hours she normally spent in Helsinki. These "picnic cruises" proved to be unpopular and they were not continued the following summer. When the EU ended tax free sales on routes between member states in July 1999, Viking Line added a stop at Mariehamn, Åland to the Helsinki—Stockholm route. As Åland is not a part of the EU tax union, Viking Line could continue tax-free sales on its ships.
In September 2000 Mariella was refitted at Naantali with rear sponsons and a new fast rescue boat. Her interior was also brought up to date, the disco moved from deck eight to deck seven, and for some time after the refit she sported the text "Updated 06/10 2000" on her hull. Another large refit was carried out in September 2006, again at Naantali, which included rebuilding of the tax free shop and parfumerie, one restaurant and disco, as well as the addition of one new restaurant next to the Food Garden restaurant.