Her position is being covered by Claire Graham, a former Oddbins buyer, who has become interim trading manager with immediate effect.
Licensed trading director Chris Lewis said: “I would like to take the opportunity to thank Xenia for all her efforts and wish her well in her new role.
“We will be concentrating on completing a smooth handover over the next few weeks.”
Irwin joined Spar as trading controller for wine in November 2010, and led the team to win a raft of awards for its wine range from a host of competitions, including the International Wine Challenge.
Before Spar, she was St Austell Brewery’s wine buyer.