Hun Manet made the announcement in a Facebook post late on Thursday, accompanied by a letter he said had been sent to the Norwegian Nobel Committee.
He hailed Trump's intervention as an example of his "exceptional achievements in de-escalating tensions in some of the world's most volatile regions".
"This timely intervention, which averted a potentially devastating conflict, was vital in preventing a great loss of lives and paved the way towards the restoration of peace," the Cambodian leader wrote in the letter.
It was a July 26 call by Trump to the leaders of both Thailand and Cambodia that broke the deadlock in efforts to end some of the heaviest fighting between the neighbours in recent history, Reuters has reported.
That led to a ceasefire negotiated in Malaysia on July 28.
The two countries agreed on Thursday to ensure no reigniting of hostilities and to allow observers from Southeast Asia.
In total, 43 people were killed and more than 300,000 displaced by a five-day conflict.
It started with small arms fire and quickly escalated into heavy artillery and rocket fire, then Thailand's deployment hours later of an F-16 fighter jet for air strikes.
The nomination had been expected after Cambodia's deputy prime minister last week announced the plan, while thanking Trump for a tariff of 19 per cent on Cambodian imports by the United States.
It was sharply reduced from the previously threatened 49 per cent that he said would have decimated its vital garment manufacturing sector.
Pakistan said in June that it would recommend Trump for the Nobel Peace Prize for his work in helping to resolve a conflict with India.
Israeli Prime Minister Benjamin Netanyahu said last month he had also nominated Trump for the award.
