Sir Mekere Morauta, whose term as Papua New Guinea prime minister ushered in sweeping political reforms prior to Sir Michael Somare coming to power five years ago, is the country's new Opposition Leader.
Sir Michael was re-elected head of the new government earlier this week.
Another former prime minister in the Opposition, Sir Julius Chan, says will focus on being governor of New Ireland, while former treasurer Bart Philemon is the deputy Opposition Leader.
Our correspondent in Port Moresby, Alex Rheeney, says Sir Julius Chan gave the small size of the Opposition - just 23 seats in the 109 member Parliament - as a factor in Sir Mekere being given the post.
"Sir Julius says while we [the Opposition] don't have the numbers compared to the Government, the Government still needs to be kept under scrutiny, still needs to be monitored and consequently they agreed that Sir Mekere Morauta will be the new Opposition Leader and will be the leader of the alternative government."
Legal action by the Opposition, challenging Sir Michael Somare's right to head the government, is due in court tomorrow.