After several years as a successful model, Diamont's first major acting role was as Carlo Forenza on Days of Our Lives.

On March 5, 2009 it was announced that Diamont would be joining the cast of the CBS daytime drama The Bold and the Beautiful in the contract role of Bill Spencer Jr. His first air date was May 12, 2009.

"Don is a versatile actor with a vast range of talent," B&B's Executive Producer and Head Writer, Bradley Bell, said in a statement, "It is my pleasure to welcome him to B&B.

In 2018 he took part in the cast of the talent show conducted by Milly Carlucci, Ballando con le Stelle (the Italian adaptation of Strictly Come Dancing / Dancing with the Stars) In 2021, Diamont announced that he would appear on The Young and the Restless as Bill Spencer Jr. in a crossover event and marking his return since Brad Carlton who is the previous cast after 12 years.

[8][9] Diamont married his long-time girlfriend Cindy Ambuehl in Eze, France on June 12, 2012, and they are parents to twin boys Anton and Davis, born December 2000.