In 1980 he served as a law clerk to Pennsylvania Supreme Court Justice Bruce W. Kauffman, who would later also be appointed as a judge on the Eastern District by President Bill Clinton).
He worked in private practice in Philadelphia from 1983 to 2004, when he was appointed by President George W. Bush to the Eastern District.
[3] From 1993 until 1995, Diamond worked as the treasurer and as the counsel for the failed 1996 presidential campaign of United States Senator Arlen Specter.
[4] On July 24, 2008, President Bush formally nominated Diamond to the United States Court of Appeals for the Third Circuit, in conjunction with Pratter's withdrawal.
In 2016, Judge Diamond rejected Jill Stein's request for a recount of Donald Trump's victory in Pennsylvania.