Andrew joined Bonhams in 1987 shortly after receiving a degree in History from Cambridge University, and was appointed Head of the Print Department two years later. In 1990 Andrew became Head of Old Master Paintings, taking responsibility for some of the company's most important sales. In 1994 he moved to Phillips to work alongside Brian Koetser in the Old Master Paintings Department. One of the highlights of this period was the discovery of a hitherto-lost masterpiece by Jean-François de Troy, which fetched £2.2 million.
In January 2001 Andrew returned to Bonhams as Head of Old Master Paintings. Successes since then have included the sale of George Stubbs's Dark Bay Thoroughbred in a Landscape for £1.9 million; a world auction record of £1.6 million for Abraham Mignon's Still Life of Flowers; the sale of Velázquez's newly discovered Portrait of a Gentleman for £3 million; and the sale of Fragonard's Portrait of François-Henri, 5th duc d'Harcourt, which at £17.1 million was a world record for a French Old Master and a world record price for an Old Master Painting at auction in 2013.