Mathew Dunn, who joined Britvic three years ago, has handed in his resignation and will serve out his notice before joining ASOS next spring.
He will fill the void created by the surprise departure of former chief number cruncher Helen Ashton earlier this year.
“I'm very much looking forward to working with the ASOS team. I'm motivated by their ambitious plans to realise the significant potential still ahead for the company,” Dunn said.
ASOS boss Nick Beighton added: “I'm looking forward to working with Mathew. He brings us a totally relevant mix of operational experience together with a history of implementing and overseeing finance systems at an international level.”
Britvic shares dropped 1.2% at the opening bell on Tuesday to 771.5p, while ASOS shares also dipped, falling 1.6% to 5,828p.