Stansfield has spent 31 years with the group, including 12 as finance director.
The company said Lyndon Davies will step down as interim chairman to focus on his role as chief executive.
Davies started as chief executive last October, taking over from Steve Cooke, who left amid a restructuring at the firm.
Hornby has been struggling to turn around the business as sales continue to fall.
Revenue for the year to March fell to £35.7mln (£47.4mln) with a reported loss before tax of £10.1mln (£9.5mln loss).
Davies’ first move as boss has been to halt the sale of large quantities of products at a discount.
In the full year results statement, he said tough decisions have been made revive the group’s fortunes. He added that national retailers “who were only a distant memory to the business have proactively re-engaged now the discounting has stopped.”
Shares in Hornby were down 4% to 32p in late morning trading.