She leaves the company next month. Welsh joined Vodafone in March 2015 from EE, where she was head of demand marketing.
Welsh has 13 years of experience in telecoms companies. She worked at BT as brand manager from 2004 to 2006.
At Vodafone, Welsh led the 2016 Christmas campaign by Grey London, which moved away from traditional tear-jerkers, and a campaign to promote the brand’s 30-day "love us or leave us" guarantee.
A spokeswoman from Vodafone said the company is recruiting for Welsh’s role, which is open to applications both internally and externally.
She added: "Vodafone is very proud of the work Caroline has spearheaded. This is brilliantly illustrated with the new brand campaign featuring Martin Freeman."