The distinctive name was put up for auction in July 2010 when its former owner, Escom LLC, went bankrupt.
Clover Holdings, a company registered on the Caribbean island of St Vincent, put in the highest bid for the domain.
At least 12 companies were understood to be bidding for the name. The price is among the highest ever paid for a domain, reports the Daily Mail.
In 2006 when Escom bought sex.com it is thought to have paid up to $14 million for it. The highest price ever paid for a domain was $16 million, which marketing firm QuinStreet paid for insure.com in 1999.
Sex.com was first registered by Gary Kremen, the owner of the dating site match.com, in 1994.
He later had the name 'hijacked' by a conman called Stephen Cohen and waged a long legal battle to retain control of the name.
Cohen ended up being jailed and fined more than $65 million for stealing the domain name.