It began in 1935 when a group of trawler owners in Hull formed a co-operative venture called British Cod Liver Oil (BCLO) Producers to exploit one of the fishing industry's most valuable by-products.

Kenneth MacLennan, previously of Lever Brothers, became General Manager of BCLO in 1936 to add relevant commercial experience to the then-board of trawler owners.

With the onset of war came a marked change of focus as the company's cod liver oil played a vital part in supplementing the meager wartime diet of the whole nation.

At the same time, the nutritional health of the nation improved along with its diet as rationing ceased, and cod-liver oil was being displaced by the introduction of pleasanter ways of taking vitamins such as Haliborange tablets (a brand the company subsequently acquired 40 years later).

In April 2015, the Sevens Seas manufacturing facility in Hull was closed,[4] and the sales and marketing of the brand was moved to Merck's headquarters in London.