Dolphin was jointly owned by its managing director David Goffin and deputy managing director Mike Wells, who will retain a minority stake in the ad sales business and will now work for SPT.
A spokeswoman for SPT refused to disclose any details about the deal (including how much it was worth or the size of its majority stake) but said she did not expect it to result in any redundancies.
The Sony Entertainment Television channel launched in the UK in April 2011 and the Dolphin deal is part of Sony's push to expand its broadcasting and ad sales business in the Europe, Middle East and Africa region.
Dolphin had 23-staff, the majority of which worked in ad sales. The ad sales business will continue to operate from the same offices in London and be led by Goffin who will report to Eddie Nelson, senior vice president for SPT, EMEA.
Dolphin TV currently sells spot ads for CSC Media Group's True Movies channel and Welsh broadcaster S4C as well as its own five channels and has teleshopping contracts with Channel 4, ITV, BSkyB, Chello and UTV.
The five Dolphin TV channels – Movies4Men, Movies4Men+1, Movies4Men2, Movies4Men2+1 and Men&Movies – will now merge with SPT's existing UK broadcasting business.
The Dolphin channels are available on Sky and Freesat and they target older men with movies and TV programmes from genres such as war, western and action films.
Goffin said: "Sony Pictures Television is a great strategic fit for our own channels and our advertising sales business.
"Naturally we are delighted to become part of SPT. The UK sales market is rapidly evolving and this allows us to invest in our core areas of spot and teleshopping sales."
There has been a lot of consolidation in the TV sales business in recent years: at the start of 2011 Virgin Media's ad sales outfit Ids closed, Channel 4 took on the sales for UKTV and Sky Media added the sales for the former Virgin Media TV channels.
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This article was first published on mediaweek.co.uk