As a soloist, Helmerson has performed with major orchestras across Europe, the United States, South America, Asia, and Australia, working with such distinguished conductors as Seiji Ozawa, Sir Colin Davis, Neeme Järvi, Evgeny Svetlanov, Esa-Pekka Salonen, Herbert Blomstedt, Kurt Sanderling, Rafael Frühbeck de Burgos, Sergiu Comissiona, and Rostropovich.

A passionate chamber musician, Helmerson served as artistic director of the Korsholm Festival in Finland from 1994 to 2001 and regularly appears at prestigious festivals including Verbier, Prades, Naantali, Kuhmo, and Ravinia. In 2002, he founded the Michelangelo String Quartet, performing internationally with Mihaela Martin, Daniel Austrich, and Nobuko Imai.

He has taught at the Hochschule für Musik und Tanz Köln and the Escuela Superior de Música Reina Sofía in Madrid. Currently, he is a professor at the Kronberg Academy in Frankfurt, a cello lecturer at the Barenboim–Said Akademie in Berlin, and a guest professor at the Hochschule für Musik Hanns Eisler Berlin.

His acclaimed recordings include concertos by Dvořák and Shostakovich, the Brahms Double Concerto with violinist Mihaela Martin, the Bach Solo Suites, and several others, all of which have been praised by critics worldwide.