The PM and girlfriend Carrie Symonds accepted accommodation for a private holiday in St Vincent and the Grenadines as a post-election victory escape.
The prime minister had faced calls to "come clean" over who paid for the luxury break on the island of Mustique after Ross, who Johnson said was responsible, denied funding the trip.
The jaunt provided Mr Johnson with a break after the election campaign which produced a Conservative landslide for the first time since the 1980s.
The entry in Mr Johnson's register of interests said that Mr Ross donated accommodation "for a private holiday for my partner and me, value £15,000".
Their £15,000 accommodation was covered by David Ross, the co-founder of Carphone Warehouse, according to the MPs' register of interests.
A spokesman for Ross, founder of mobile phone retailer Carphone Warehouse, told the Daily Mail that the businessman had helped find a villa for Johnson, but had not paid for it.
Earlier in the day the PM had been urged to reveal who funded the trip, or face a parliamentary inquiry.
"So Boris got the use of a villa that was worth £15,000, but David Ross did not pay any monies whatsoever for this".
The main opposition Labour Party wrote to the parliamentary commissioner for standards demanding an investigation, saying questions had been left unanswered. Johnson, who had wanted to minimize any disruption from his long-planned cabinet revamp, quickly replaced Sajid Javid with his deputy Rishi Sunak, a loyal supporter of the prime minister who is often put before the media to sell government policy.
The trip was also added as a "benefit in kind" and the name of the donor was listed as "Mr David Ross".
A No. 10 spokesperson said the Prime Minister had followed "all transparency requirements".
He added: "Transparency is crucial to ensuring the public have confidence that elected members of this House have not been unduly influenced by any donations or gifts that they may receive".