The company, which spans Europe and Africa, said it had conducted a rigorous internal and external search before choosing the insider who has been chief financial officer since 2018.
She stepped into the top role on an interim basis after Nick Read abruptly left in December, when he agreed with the board that it was the right moment for a new leader.
"To realise our potential Vodafone needs to change," she said. "We know we can do better. My focus will be to improve the service for our customers, simplify our business and grow."
Her strong backers included institutional investors such as biggest shareholder Emirates Investment Authority, which has built up a 14.6% stake, a source told Reuters.
Shares in Vodafone were trading up 1.2% at 95 pence.
Emirates Investment Authority also owns telecoms group Etisalat. Hatem Dowidar, Group Chief Executive Officer at e& (Etisalat) offered his congratulations to Della Valle on LinkedIn.
CCS Insight analyst Kester Mann said appointing a close aide of Read to the top job suggested little deviation in strategy.
"This may not go down so well with people pushing for a fresh approach to running the embattled company, but it does give Vodafone a safe pair of hands during a challenging time," he said.
Della Valle, who is Italian like former chief executive Vittorio Colao, joined Omnitel Pronto Italia - which later became Vodafone Italy - in 1994, and held roles in marketing and analytics before moving to finance.
Her immediate predecessor Read had pinned his hopes on the consolidation of Europe's fragmented telecoms markets but he struggled to turn intention into action.
Investors' frustration was reflected in a 45% fall in the company's share price during his four-year tenure.
After he left, some investors and analysts said an outsider was needed to shake up the group.
Analysts at Berenberg said in January that they believed "Della Valle would be viewed by investors as a 'continuity' appointment, which is not what we believe shareholders are looking for".
Della Valle's first major deal is likely to be the tie up between Vodafone UK and Hutchison's Three in Britain, expected imminently.
