Lennart's later screen credits include A Life of Her Own, Love Me or Leave Me, Merry Andrew, The Inn of the Sixth Happiness, Please Don't Eat the Daisies, The Sundowners, and Two for the Seesaw.
In 1949, he became first trumpet with the MGM film studio orchestra, playing on all the major MGM soundtracks from the Golden Age of Hollywood including An American in Paris, Singin' in the Rain, Gigi, West Side Story (at United Artists), My Fair Lady (at Warner Bros.), Two for the Seesaw and Bye Bye Birdie (at Columbia Pictures), along with many others.
The Harris occasionally presented live performances during this period, such as a production of "Two for the Seesaw" starring Ruth Roman.