He is a member of his aunt Baroness Elisabeth-Anne de Massy’s organization, All-sports Country team (A.S.Co.T., Team Monaco captain) of the tennis tournament. He also serves as founder and director of the board to his wife's organization, ConservationGuardians.
After obtaining his BA in business, Sébastien moved to Lima, Peru to work for Grana y Montero Petrolera. After living in Peru he moved back to Monaco and started his shipping career with the V. Ships Group. This brought him to live in London, Singapore and Paris. In 2005 Sébastien founded Madison Marine and today controls a fleet of merchant vessels.
In 2008 he co-founded Transport & Commodities which is based in Monaco and manages shipping, upstream and mining ventures.
He is a citizen of Monaco, where he resided with his wife Donatella, and four daughters until 2011 or 2012, now the family resides in South Africa. His daughters are:
Because he and daughters *technically* lost their place in succession with the death of Prince Rainier in 2005, she and her family are known to keep out of the main limelight. However, in more recent years, they have come to a few family events. In 2008,he, his wife, and their two older daughters (who were 6 years old and 7 years old at the time) attended the 32nd annual International Circus Festival of Monte Carlo, and they sat in the royal box with the rest of the Grimaldis. They also attended the event in 2011. In July 2011, he attended his mother's cousin's wedding ceremonies with his wife and three elder daughters. He also attended the Eagles and JM Jarre concerts (sitting in front of Princess Charlene). That November, he and his wife appeared with the family during the National Day festivities, at the church service, during the honor guard ceremony ( behind his wife, who is across and behind Princess Stephanie) and of course, on the balcony. In 2015, he and his wife were present during the baptism of the Princely Twins and his whole family was present for Prince Albert II's 10 year celebrations (Sébastien can be seen dead center, the really tall guy, his two daughters Christine and Andrea can be seen in front of him next to Charlotte Casiraghi, and his 3rd daughter Alexia is to his right between Charlotte and Pierre. I also think that his wife Donatella is directly behind-thus hidden behind-Charlotte.).
He shares a birthday with the son of his maternal first cousin 1x removed, the elder son of Prince Albert of Monaco, Alexandre Coste Grimaldi.