When he was asked to join the world-famous recording group 'The Lettermen', Mark accepted and performed for 11 years with the group. During that time, the group recorded several albums and CDs. There was a campaign to put forward the group's most recent recording, New Directions 2010 with the Les Brown Jr. Orchestra, for three Grammy nominations. In 2001, the Lettermen were inducted into the Vocal Group Hall of Fame, and in early 2020, the group was awarded a star on the Hollywood Walk of Fame.