The July 18-22 national online poll found that 41 percent of likely voters supported Clinton, while 38 percent supported Trump. Given the poll's credibility interval of about 4 percentage points, Trump and Clinton should be considered to be about even in the race.
Just before Republicans opened the convention on Monday, Trump had trailed Clinton by nearly 10 percentage points in the poll.
The New York businessman-turned-politician formally accepted the Republican nomination for the Nov. 8 presidential election during a convention at which the party at times struggled to show unity.
The week started with a dustup between convention leaders and delegates who wanted to change the party's rules to derail Trump's nomination. Later in the week, Senator Ted Cruz of Texas, who dropped out of the nomination race in May, refused to endorse Trump in a prime-time speech.
Yet, on the final night of the convention, Republicans gave Trump a standing ovation as he pledged to take back a country that he said is plagued by crime, terrorism and ineffective leadership.
Party conventions are partly meant to introduce the candidate to the country, and nominees tend to get a boost in opinion polls afterward. In 2012, then-Republican nominee Mitt Romney rose by about 5 percentage points in the Reuters/Ipsos poll after his party's convention.
Clinton, who is expected to be formally nominated by her party at its convention in Philadelphia next week, has led Trump most of the year in the poll.
The last time Trump drew about even with Clinton was in mid-May, after his last two rivals for the Republican nomination dropped out of the race and party leaders started to get behind his campaign.
The Reuters/Ipsos poll was conducted in English in all 50 states with 1,036 likely voters.