The tribunal, created in 2006 to prosecute leading Khmer Rouge members, recently held its first trial
Cambodia's Khmer Rouge war crimes court has named Andrew Cayley as its new international prosecutor.
The genocide tribunal appointed British-born Mr Cayley several months after the resignation of his Canadian predecessor, Robert Petit.
Mr Cayley recently defended the former Liberian President Charles Taylor at his war crimes trial.
Cambodian King Norodom Sihamoni formally appointed Mr Cayley, according to a court statement.
American Nicholas Koumjian was appointed reserve co-prosecutor.
Mr Cayley has spent the last two years in private practice, during which time he defended Mr Taylor.
WHO WERE THE KHMER ROUGE?
Maoist regime that ruled Cambodia from 1975-1979
Founded and led by Pol Pot, who died in 1998
Abolished religion, schools and currency in a bid to create agrarian utopia
Up to two million people thought to have died from starvation, overwork or execution
Before this he worked for the International Criminal Court investigating crimes in Darfur, and served at the International Criminal Tribunal for the former Yugoslavia.
His appointment was welcomed by court observers who stressed the importance of having a permanent international prosecutor in place.
Critical decisions "should be made by the international prosecutor who will have the responsibility for carrying them out," Heather Ryan, court monitor for the Open Society Justice Initiative, told the French news agency AFP.
The UN-backed tribunal incorporates mixed teams of foreign and Cambodian judges, prosecutors and defenders.
A verdict in Comrade Duch's trial is expected early next year
Disagreements among the legal teams have been known to lead to frequent delays, whilst allegations of corruption have damaged the tribunal's credibility.
Indeed, the resignation of Mr Petit came after a dispute with Cambodian co-prosecutor Chea Leang over whether to pursue more suspects of the late 1970s communist regime.
Mr Petit denied any connection, saying personal reasons were behind his resignation.
The tribunal, created in 2006 to prosecute leading Khmer Rouge members, recently held its first trial, for prison chief Kaing Guek Eav, better known as Comrade Duch.
The prosecution is seeking a jail term of 45 years, with five years deducted to take account of Duch's co-operation and time already served.
Duch is the first of five leading Khmer Rouge figures to face the UN-backed tribunal.
The joint trial of four other - more senior - Khmer Rouge leaders is expected to start in 2011.
The court is also investigating whether to open more cases against five other former Khmer Rouge officials.
Up to two million Cambodians died under Pol Pot's Khmer Rouge rule in the 1970s.