Sommerville reportedly has had little conducting experience outside New England Conservatory, where he is on the faculty, and the Tanglewood Festival, where he has led small ensembles over the past few summers. He has twice appeared with the HPO as a guest conductor, most recently during a pops concert in September.

"This is a career transition for him," HPO executive director Alex Baran told the Globe. "He's embarking on a conducting career with us."

Sommerville, who begins his tenure on July 1, will conduct the orchestra for nine weeks next season, while keeping his Boston Symphony hornist position. His first performance as the HPO's music director designate takes place on May 26.

Sommerville joined the BSO as principal horn in 1998. In the fall of 1997, he played with the Toronto Symphony. From 1986 to 1991 and again from 1995 to 1997 he was associate principal horn of the Montreal Symphony. He has also been solo horn with the Canadian Opera Company and Symphony Nova Scotia.