Observations: New show was five years waiting in the wings

The artist Keith Holmes paints actors, directors – even a show's technical crew – during rehearsals and backstage in the West End.

Now his 67 oil paintings, including ones of actor Mark Rylance holding a megaphone rehearsing Jerusalem at the Apollo Theatre, and Michael Grandage with his arm outstretched while directing Don Juan in Soho at the Donmar Warehouse, along with 45 charcoal drawings – all created over a five-year period, will be up for grabs in his first London show later this month.

According to Grandage, who allowed him to be artist-in-residence at the Donmar in 2005, Holmes has "a wonderful eye" for "capturing theatre in action", whether it's behind the scenes or in performance.

"Best of all, he makes us look at our work in different ways and always offers a poetic intensity to his subjects," says Grandage. "It is wonderful to bring together so much of his theatre work in one exhibition."

A painting of Christian Slater playing the horrible boss Buddy Ackerman in Swimming with Sharks at the Vaudeville Theatre shows the actor in a red striped suit and looking sly for the role, while holding his mobile phone. "It's my favourite painting," admits Holmes. "He actually posed for it, which is not something that usually happens."

Another painting of the director Thea Sharrock shows her dancing with flowers behind her on set of A Voyage Round My Father at the Donmar. "She had just given birth a few months before and was an absolute bundle of energy. She was demonstrating what she wanted from the cast."

Armed with a small sketchpad, Holmes usually amalgamates many of the repetitive scenes he observes into one final painting which, he says, "slowly evolves". "I could never have got Grandage to pose for me. This way I capture the essence of a person or a scene realistically."

Holmes was artist-in-residence at the Science Museum in 1994 before he was embedded with the Royal Marines. He went on to record the impact of landmines as artist-in-residence for the Mines Advisory Group in Cambodia, Laos and Kosovo in 1999, and then found his niche in the West End. "It is easier painting actors in the West End than doing dramatic leaps out of helicopters," he says.

When Grandage offered Holmes a free reign at the Donmar, all he told the artist was "come and enjoy yourself". Now his paintings will be sold for £900 to £6,000 each. "It's my first exhibition. I didn't want to do it in dribs and drabs because it loses its momentum."

Holmes observes every phase of the production process, from set-building, rigging, technical rehersals to the final show. "Mine is a fly on the wall approach," he says. "In all the productions I've sat on I have been amazed by the total dedication, professionalism and teamwork of everybody involved."

Behind the Scenes', Art Galleries Europe, London W1 (www.artgallerieseurope.com) 21 May until 26 May