Nxasana, from the KwaZulu-Natal division of the high court, would start his new role on October 1, spokesperson Mac Maharaj said in a statement.
"Nxasana currently practises as an attorney with a wealth of experience in criminal litigation, coupled with his having occupied senior positions in the legal profession – including the chairpersonship of the KwaZulu-Natal Law Society," said Maharaj.
The NPA has been without a permanent chief since November 2011, after Menzi Simelane's appointment was declared invalid.
Simelane's appointment as NPA boss was deemed "inconsistent with the Constitution and invalid" as Zuma did not apply his mind in the decision.
Simelane, who Zuma placed on paid leave after the decision, was appointed NPA boss in 2009 after the 2008 Ginwala inquiry severely criticised him.
The inquiry, which investigated the fitness of former NPA head Vusi Pikoli's ability to hold office, labelled Simelane's evidence before the inquiry as "contradictory and without basis in fact or in law" and blamed him for suppressing a disclosure of information. – Sapa