Born in Porvoo in 1946, he lives on the island of Kökar, Åland.

Westerberg published 15 collections of poetry since 1967. He translated works by e.g. Samuel Beckett, Bo Carpelan, Gunnar Ekelöf, Tua Forsström, Ted Hughes and Tomas Tranströmer.

Prizes: The Finnish State Literatur Award 1970,1986; The Finnish Writer's Union's Prize 1978; The Finnish State Translation Award 1984;  Suuri Suomalainen Kirjakerho Award 1986; The Dancing Bear Award for Translation 1994; Eino Leino Prize 1995; The Great Prize of Finlands Svenska Författarförening 1998; The Fund of Irene and Kalevi Sorsa Translation Prize 2005; Mikael Agricola Award 2007, Finnish Association of Translators and Interpreters; The State Pension for Artists 2007.