And yet, some of the portraits he is most well-known for are of some of the world's most famous people, including Brad Pitt, Liam Neeson and Ed Sheeran - which is currently hanging in the National Portrait Gallery as part of its latest blockbuster, Shakespeare to Winehouse.

But while the artist may be known for these works, Davidson never sought out any of his famous faced subjects (or, in fact, many of his portraiture subjects in general).

In a streamed conversation with the National Portrait Gallery on Monday, the artist spoke about how he didn't seek out to do celebrity portraits. They almost all happened by chance.

In the case of Ed Sheeran, it came about after the singer's father and grandmother came to view a point Davidson had made of Belfast Olympian Lady Mary Peters. Sheeran's grandmother happened to be a childhood friend of the athlete.

From there, conversations started about Davidson doing a portrait of the singer, which then continued at Sheeran's Belfast concert that was happening that same night.

"Ed loved the work, really related to it and said that he would love me to paint him. And that's how it was done," Davidson says.

"So I spent two to three hours with Ed. We chatted. I do not want the sitter to give me their best side and look in one particular direction. I want to see how the face works. I want to see how the face works when the sitter is happy or talking about melancholic things or talking about reflective things, or even when they're being quiet."

Davidson's work is all about capturing people in the moment - and in the case of his celebrity sitters, it's also about finding the humanity behind the fame.

For his first time painting Brad Pitt, for example, the sitting happened in a hotel room just after the actor got off a transatlantic flight. Pitt was jet-lagged and that was the moment Davidson captured him.

But it was such a different view of the actor that some commented that it didn't look much like the actor - to which Davidson says, when was the last time you saw Brad Putt post transatlantic flight?

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"I'm not interested in celebrity at all. Never have been. Part of me despises it, actually. Celebrity is fake," Davidson says.

"And also celebrity in the case of the people I'm painting is not self-imposed. Celebrity imposed by virtue of what their career is, what their profession is or by the outside world imposing celebrity onto them ... that's what's interesting about painting people that the world calls celebrities ... because you've got a facade to strip away.

"Take the portrait of Liam [Neeson] ... we were talking in the sitting about art and at one point, he was saying that he didn't have an interest in art until his wife [Natasha Richardson] introduced him to art. And this was just shortly after his wife had tragically passed away [in 2009].

"And he became really moved as he was talking about his wife introducing him to art and that love and that passion continues to this day. And that's the portrait that I made. It's possibly one of the saddest paintings I've ever made. In some ways, it's of a grieving human being. And the fact that it's Liam Neeson is secondary to it."

Despite the big names Davidson has painted, the artist didn't consider himself a portraiture artist until later in his career. Instead, he opted to paint cityscapes, particularly of his hometown of Belfast, and of shop windows which depicted both what was beyond the pane of glass and what was reflected in it.

Funnily enough, it was the techniques which he picked up exploring these works that would go on to help him with his portraiture work, starting with his 2006 portrait of Belfast performer Duke Special.

"If you have a look at the eyes in this, this is drawn directly from the way that I treated the glass. So I'm painting these eyes in exactly the way that I treated those oil paintings of the shop fronts," Davidson said.

"The hair, the dreadlocks, the flesh is treated as I would the architecture. And even the scribbly lines left in the hair are very, very much the way that I would've treated the Belfast paintings."

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