Hilary won the Theakstons Old Peculier Crime Novel of the Year Award in Harrogate on Thursday.
Radio Times TV editor Alison Graham, who was one of the judges, described the book as "an emotionally exhausting and powerful story".
US author Sara Paretsky, who created detective VI Warshawski, received an outstanding contribution honour.
The accolades were handed out at the start of the North Yorkshire town's annual crime writing festival.
Shetland and Vera writer Ann Cleeves, this year's festival programming chair, said the crime novel of the year shortlist had been "really strong" this year.
The panel had felt Hilary's winning book was "so finely written and tightly written", she said.
Someone Else's Skin, a thriller that tackles domestic violence and so-called honour crime, is the first in a series of novels featuring Det Insp Marnie Rome.
"The author was able to conjure up atmosphere in very few lines," Cleeves said. "The subject matter was well done and well plotted."
The other books on the shortlist were:
Sara Paretsky was chosen for the outstanding contribution to crime fiction award after her 23-year career writing about VI Warshawski, a female private investigator from Chicago.
Actress Kathleen Turner played VI Warshawski in a 1991 movie based on the Deadlock novel and in a BBC Radio 4 adaptation.
VI Warshawski was "a real game changer", Cleeves said. "This was a woman who didn't just solve crimes but was like an action hero in a sense."
Paretsky "really changed the way that readers thought about female writers", Cleeves said.
"When she started writing, it was pretty well unheard of to have a strong female protagonist," she added.
Paretsky also set up Sisters In Crime, an organisation to support female crime writers around the world.

The actor is due to star in a fifth Indiana Jones film, which will be released in 2019.
Ford told the BBC: "I've always thought there was an opportunity to do another. But I didn't want to do it without Steven [Spielberg].
"And I didn't want to do it without a really good script. And happily we're working on both.
"Steven is developing a script now that I think we're going to be very happy with," he said of Spielberg, who is directing the film.
Spielberg directed the four previous Indiana Jones films, which were all produced by Star Wars creator George Lucas.
Ford first appeared as Indiana Jones in Raiders of the Lost Ark, released in 1981.
He then starred in three subsequent films, most recently in 2008's Indiana Jones and the Kingdom of the Crystal Skull.
Ford was speaking to the BBC ahead of the DVD release of Star Wars: The Force Awakens, the film in which he reprised his role as Han Solo.
When asked whether Han Solo, who is killed in the film, could return in some form to future movies in the franchise, Ford replied: "Anything is possible in space.
"I wanted Han Solo to sacrifice himself for the good of the other characters to bring some gravitas to the story."
Speaking about his involvement in the film, Ford said: "I was very pleased to have the opportunity to work with the other characters, to work on a script that I had real confidence in, with actors that were a dream to work with, with a director that had a very sure and generous hand, and it was altogether a pleasure."
But Ford said he does not feel an emotional connection to the characters he plays.
"I hope I bring an emotional understanding of the characters and something the audience will recognise," he said.
"I want the audience to experience the character, not to feel that they know him but to be involved in seeing what happens to him."
Star Wars: The Force Awakens became the UK's biggest film of 2015 after just 16 days of release, with takings of Â£94.06m.

31 March 2017 Last updated at 09:10 BST
That's because she has a very strong type of anxiety called selective mutism.
But she's started taking a special music class which has helped her to speak at school.
Meet Ruweyda by watching our video.
You can find out more about what anxiety is and how it can affect you by reading our guide, here.
Author Sarah Hilary has won one of the UK's top crime-writing awards for her debut novel, Someone Else's Skin.
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Harrison Ford has said he did not want to star in a new Indiana Jones film without director Steven Spielberg.
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Ruweyda is seven years old and has only recently said her first words at school.