Formerly the director of brand marketing, Fielding will now pursue non-executive directorships and work on her own projects, including writing a book.
A spokeswoman for Vodafone confirmed the operator had yet to find a replacement.
Fielding, celebrated last year as one of Marketing's Power 100, oversaw campaigns that gave a more sympathetic face to the operator.
Jeroen Hoencamp, CEO for Vodafone UK said in a statement: "In her two years with us, Daryl undertook a major strategic review and led the transformation of our brand marketing.
"Her strategy and advertising campaigns have resonated with our people and consumers and have led to significantly increased brand measures in our marketplace."
He added: "Daryl always made it clear that once she had completed this piece of work she intended to pursue other interests and we wish her well as she pursues various non-executive directorships and gets down to writing her book."
An emotive TV ad from March last year by Grey London featured real fire-fighters using Vodafone's network to contact loved ones - though it was subsequently banned by the UK's advertising watchdog for being misleading.
Fielding joined Vodafone in early 2013 from her own consultancy, and previously held senior marketing roles at Kraft, the Independent and Ogilvy.