About 10 executives from top European banks took part in the meeting, according to a British official, during which Kerry sought to allay bankers' concerns following past fines for lenders for breaking Iran sanctions.
"We want to make it clear that legitimate business, which is clear under the definition of the agreement, is available to banks," Kerry said.
Also present were Lord Lamont, trade envoy to Iran and British secretary of state for business Sajid Javid.
The United States and Europe lifted sanctions in January under a deal with Iran to limit its nuclear programme, but other U.S. sanctions remain, including a ban on Iran-linked transactions in dollars being processed through the U.S. financial system.
Ayatollah Ali Khamenei, the most powerful figure in Iran, has blamed the delays in the resumption of trade squarely on the United States.
"The U.S. Treasury ... acts in such a way that big corporations, big institutions and big banks do not dare to come and deal with Iran," Khamenei said in March.
European banks have expressed their own scepticism about resuming support for companies conducting business in Iran.
"Certain EU and US sanctions against Iran and additional non-sanctions related restrictions remain. Therefore, Deutsche Bank continues to generally restrict business connected to Iran," Deutsche Bank said in a statement ahead of the meeting.
Kerry said the purpose of the meeting in London was to listen to such fears and attempt to address them. (Reporting by David Brunnstrom, Arno Schuetze and Kate Holton; Writing by Lawrence White; Editing by Tom Heneghan)