Ian Paisley and Martin McGuinness have spent more than an hour talking to US President George W Bush.
The two men have been in the United States for five days
They had been scheduled to have 15 minutes for the White House meeting in the Oval Office.
President Bush said he would do his best to help Northern Ireland. The meeting marks the climax of the pair's five-day visit to the United States.
They are now returning to Northern Ireland after declaring their five-day investment mission a great success.
During the meeting, President Bush was asked to remember Royal Irish Regiment soldiers, who are serving in Iraq.
Speaking immediately after their meeting with President Bush, Mr Paisley said the five-day investment mission had been a great success.
"I couldn't leave this city in a better frame of mind," he said.
"It's a very happy way we leave. This has been a tremendous meeting for us. This has been a cracker of a meeting."
Mr McGuinness added that he was tremendously encouraged.
"I think people here are delighted and overjoyed, as we are delighted and overjoyed."
The two men also had half an hour of talks with the head of the national security council Stephen Hadley.
Earlier, Senator Hillary Clinton said there would be an open door for the first and deputy first minister if she were elected to the White House.
Mrs Clinton said she hoped to be able to return to Belfast next year.
She said Americans were ready to help the new administration.
"I am going to do whatever I can as president, to make sure that the first minister and the deputy first minister know that they have an open door in the White House," she said.
"They have as much support and encouragement as we possibly can provide, not only from our government but from, as the first minister said, our private sector and I would go so far as to say even Americans individually."
She was among a group of congressman and senators, along with Ted Kennedy, who passed a resolution formally welcoming their visit to the US capital.
Another congressman, Jim Walsh, has also proposed that formal links be established between Stormont and Congress.