From 2002 to 2013, Foster was the Music Director of the Gulbenkian Orchestra of Lisbon, Portugal. He also served as Music Director of the Orchestre National de Montpellier and the Opéra National de Montpellier from 2009 to 2012. In February 2012, Foster was announced as the next music director of l'Opéra de Marseille and the Orchestre Philharmonique de Marseille. As of 2019 Foster is the Artistic Director and Chief Conductor of the Polish National Radio Symphony Orchestra (NOSPR).
Foster is particularly noted as an interpreter of the works of George Enescu, and has made a comprehensive survey of commercial recordings of Enescu's music. In 2003, he was decorated by the Romanian President for services to Romanian Music.