Iran has vowed to restart nuclear activities it set aside under the deal if the United States breaks the agreement by reapplying nuclear-related sanctions.
Trump sounded as opposed to the deal as ever before the meeting, telling reporters: "It's insane. It's ridiculous. It should never have been made."
But Trump added that "we'll be talking about it" and noted that the discussion is important to Macron.
Afterward, Trump called the Iran discussion "substantive" and said he looks forward to "doing something."
It was not clear what he meant.
Macron is the emissary for a European proposal to add safeguards that address some of Trump's main complaints about the deal reached under his predecessor, Barack Obama.
The proposed side agreements between the United States and Europe could push for international inspection of Iranian military sites and apply sanctions if Iran crossed certain thresholds in its missile testing.
Such side deals would not change the terms of the international pact itself, and would not bind co-signers Russia and China.
"We'll see. People know my views on the Iran deal. It was a terrible deal," and the United States could have struck a better one, Trump said.
Macron spoke in French and then in English.
"The Iran deal is an important issue, but we have to take a far broader picture which is security in the overall region," Macron said. "What we want to do is to contain Iran and its presence in the region."
Trump readily agreed.
"It just seems that no matter where you go, especially in the Middle East, Iran is behind it, wherever there's trouble. Yemen, Syria, no matter where you have it, Iran is behind it," Trump said.
"And now unfortunately, Russia is getting more and more involved. But Iran seems behind everything where there's a problem. And we just have to take a look."
French efforts to counter terrorism in the Middle East are part of Macron's approach in asking Trump to revisit his opposition to the deal.
Macron is betting that his personal bond with Trump and pragmatism about sharing the global security burden can help his case that the Iran deal is worth preserving.
It is working to keep a cap on the Iranian programme, Macron and other advocates argue, even if its terms do not cover missile development or alleged support for extremism and terrorism.
"We've come a long way, just the two of us, just in understanding, and we talked about Iran, we talked about Syria, we talked about a lot" of difficult issues, Trump said after his first meeting with Macron. "And we think we have solutions to a lot of them."
Macron noted that the session covered climate change and the US withdrawal from the Paris climate accord, but he did not give details.
Trump also said North Korea wants to have its summit with the United States "as soon as possible," and he called leader Kim Jong Un "honourable" in his dealings ahead of the planned meeting with Trump.
The White House has said that meeting could take place in late May or early June.
