In the previous week’s poll, Harris, 59, and Trump, now the elder in the presidential race at 78, were tied at 44 percent.
Both results are within the polls’ margins of error.
The new surveys followed both the Republican National Convention, where Trump formally accepted the party’s presidential nomination, and Biden’s leaving the race.
Harris’s performance in the polls, bolstered by the excitement among Democratic voters about the shakeup in the race, shows her apparently neutralizing the bounce that a nominee gets in the days after his or her party’s nominating convention.
In a PBS News/NPR/Marist poll conducted Monday, Trump edges Harris with 46 percent to 45 percent of US registered voters, with nine percent undecided.
If third-party candidates or independents are included in the contest, Trump and Harris are tied at 42 percent, with the others far behind.
The PBS News survey notably found that 87 percent of all Americans think Biden’s decision to drop out was the right move, a view that crossed partisan and generational lines.
Both surveys come in the aftermath of Trump surviving a shock assassination attempt at a Pennsylvania rally on July 13.
Trump maintains a very narrow advantage of 1.6 percentage points against Harris, according to an average of polls collated by RealClearPolitics.