Clinton enjoys 51% of support among Americans, up by seven points from May, compared to Trump's support at 39%, which is down by seven points, according to the Washington Post-ABC News poll.
This is Clinton's biggest lead over Trump since last fall and is a dramatic reversal from the May poll, in which Trump led Clinton slightly by 46% to 44%, Xinhua news agency reported citing the poll.
The poll discovered that 56% of American voters believe Trump stands against their beliefs, while 64% said Trump does not have the necessary credentials to be president.
Clinton's lead over Trump narrows to 10 points by 47% to 37%, when the two third-party presidential candidates were mentioned in the poll.
Libertarian Party's Gary Johnson gains 7% of support, while Green Party's Jill Stein garners only 3%, according to the poll.
The controversial comments on women, minorities and Muslims made by Trump may have contributed to his recent slide in the poll, as the majority of American voters regard them as biased.
Overall, 66% of Americans think Trump's remarks as "unfairly biased," while only 29% said they are "not unfairly biased".
Even among the Republicans, 41% think Trump's remarks are "unfairly biased", while 53% said they are "not unfairly biased".
Trump has been criticised recently for publicly attacking a Mexican-American judge overseeing the Trump University fraud case.
The poll found that 68% of Americans regard Trump's criticism of Judge Gonzalo Curiel as racist and 85% said they were inappropriate.