Humphrey joined the wholesaler in 2002 and had made an "outstanding contribution during a period of unprecedented change", Smiths News said. He previously worked for 22 years at former parent company WH Smith.
"Alan has led the finance function superbly and his counsel and guidance during an unprecedented period of revenue and profit growth for the company have been invaluable," said CEO Mark Cashmore.
In a separate move, commercial director Jon Bunting has been promoted to chief operating officer and will join the board of directors from 1 April. He has been with Smiths News since 1994 and will lead the company's drive to strengthen its current market position and diversify into new market segments.