She grew up in Monaco, attending the International School of Monaco, earning the International Bacclaurate in 2004.
Mélanie is a prominent business woman in Monaco, she is presently Agribras’ Head of Investor Relations. She is an adviser for Giersch Ventures, a financial advisory boutique, and a co-founder with Luiz Macambira of The Macmas Group, an investment advisory, real estate development and event promotion group.
Miss Costello de Massy sits on the Committee of the Monte-Carlo Country Club and is involved in the organization of the Monte-Carlo Masters Tennis Tournament. She is fluent in French and English, as well as speaking some German and Italian.
As a granddaughter of Princess Antoinette, she was in line for the Monégasque throne until the death of her great uncle in 2005. Presently, she is a member of the pool that may be selected by the National Council if for some reason the present line fails. In addition to her business and civic activities in Monaco, she is regulatory present along side her mother at various other events in Monaco including the Family Appearance on National Day (seen here in red, behind Princess Caroline) and The Red Cross Ball (between Gareth Wittstock and her mother).