In 1940 he formed the Almanac Singers with Pete Seeger and Lee Hays, later adding Woody Guthrie.
During the period of the Hitler-Stalin pact from 1939 to 1941, the group also sang songs attacking Franklin D. Roosevelt as a warmonger and opposing Britain's war against Nazi Germany.
After the Almanac Singers disbanded in 1942, Lampell wrote the lyrics for The Lonesome Train, a ballad opera on the death of Abraham Lincoln, with music composed by Earl Robinson.
He wrote the screenplay for the marriage guidance film This Charming Couple (1950) using the pseudonym H. Partnow.
In 1966, he was awarded an Emmy for his teleplay for the Hallmark Hall of Fame drama Eagle in a Cage.