The bookish and conservative Clement will leave his post June 2 -- a few weeks before the nation's highest court adjourns for summer break.
A Justice official said Clement has no immediate plans other than spending the summer with his children.
Attorney General Michael Mukasey called Clement ``one of the nation's finest appellate lawyers.''
''I will miss not only Paul's superb advocacy on behalf of the United States, but also his wise counsel and keen legal analysis,'' Mukasey said in a statement.
As the department's No. 4 official for three years and principal deputy solicitor general for four years before that, Clement argued 49 cases before the Supreme Court.
The court ruled against Clement in Hamdan v Rumsfeld, the case that sent the White House back to Congress for approval for its Military Commissions at Guantánamo.
The court is also currently deciding another Guantánamo case, involving the limits of detainee rights in civilian federal courts.
Yet the Justice Department said the court sided with Clement in ''the vast majority of cases,'' including:
• Gonzales v. Raich, upholding Congress' right to ban medicinal marijuana over state laws allowing it.
• Gonzales v. Carhart, declaring laws prohibiting so-called partial birth abortions as constitutional.
• McConnell v. FEC, which found that disallowing soft money in political campaigns did not violate protections on free speech.
• Clement also represented the government in Rumsfeld v. Padilla, arguing that the president could detain a U.S. citizen who had been designated an enemy combatant. The Supreme Court did not reach a decision in the case, ruling that it had been improperly filed.
The court's current term will conclude at the end of June. Clement will leave before then but plans to have all the government's court filings on pending cases done before he goes.
