Alex Beech, 44, admitted conspiracy to defraud, at Inner London Crown Court, after an international investigation.
Ulrik Nielsen, 57, from Gentofte near Copenhagen, also admitted the offence.
While the pair pleaded guilty, discussions are ongoing about the precise dates of the charge, the number of shipments involved and the financial loss to others.
A third man, Andronicos Sideras, 54, of Southgate, north London, pleaded not guilty and will go on trial on July 3.
The men were accused of dishonestly arranging for beef and horsemeat to be combined for sale as beef to be sold in the UK’s meat industry.
The offence is said to have taken place between January 1 2012 and October 31 that year.
In 2013 UK supermarkets were rocked by the horsemeat contamination crisis, with products labelled as beef and other meats found to contain various amounts of horse flesh.
The trial of Sideras is expected to last no more than three weeks.
Nielsen and Beech will be sentenced after the trial.