The survey found 66 percent of Americans have a favorable opinion of the former president, whose ranking has averaged 56 percent since his inauguration.
His unfavorable rating was a near-record low 28 percent.
The poll found equally high favorable ratings for his wife, Hillary.
Gallup said Bill Clinton is liked across all major age groups, with broad support from independents and Democrats.
Republicans have changed the most in their opinions of Clinton. The poll reported they gave him a 44 percent favorable rating, compared to only 18 percent in August 2008.
Democratic Party officials hope Clinton's popularity will give a boost to President Barack Obama's re-election campaign. He's less popular than the former president, with a popularity rating of 54 percent. Clinton is scheduled to give a major address at the Democratic National Convention in September.
The poll was conducted July 9-12 with 1,014 people randomly selected for telephone interviews in every state and the District of Columbia. The margin of error is 4 percentage points.