Kerry said the measure approved yesterday by the Senate Foreign Relations Committee, which raises the threshold for critics in Congress to block any accord with Tehran, made him "confident" ahead of a June 30 deadline.
"Yesterday there was a compromise reached in Washington regarding congressional input," he told reporters at a G7 foreign ministers' meeting in Germany.
"We are confident about our ability for the president to negotiate an agreement and to do so with the ability to make the world safer."
However under the legislation, which now heads to a full Senate debate and vote, the total review period would be reduced to 52 days, from the 60 days in earlier drafts.
Contentious language obliging President Barack Obama to certify to Congress that Iran was not engaging in terrorism was also removed from the bill.
Global powers must resolve a series of technical issues by the June 30 deadline for a final deal, including the steps for lifting sanctions on Iran, and remaining questions over the possible military dimensions of its nuclear programme.
The host of the G7 meeting in the northern German city of Luebeck, German Foreign Minister Frank-Walter Steinmeier, said talks between representatives of the United States, Britain, France, China, Russia, Germany and Iran "on a final agreement will begin next week".
He did not cite a date or location.
The aim is to pave the way for "a meeting at the level of the foreign ministers at a later point in June" to seal a final accord.
