The U.S. currency fell to one-week lows against the euro and Swiss franc, and dropped against commodity currencies such as the Australian and New Zealand dollars as well as the Norwegian crown.
The 90-minute televised debate between the two U.S. presidential candidates at 9 p.m. EDT (0100 GMT) will be watched by investors looking for guidance on the candidates' prospects.
"The debate is so much awaited because of all the political tensions going and also because economically both candidates have different visions for the country," said Juan Perez, senior currency trader, at Tempus Inc in Washington.
"There is a lot more volatility on the domestic side than on the international side. Global sentiment is also a little better than that in the U.S. and so it's making sense that investors are moving away from the U.S. dollar," he added.
In afternoon trading, the dollar index fell 0.3% to 93.879<=USD>, after hitting a two-month peak on Friday.
The greenback also added to losses, as investors felt a little more confident getting out of the safe-haven currency after data showed U.S. consumer confidence rebounded more than expected in September, as households' views of the labor market improved.
The dollar was also weighed down earlier by currency flows in the options market as well as for month end, said Erik Bregar, head of FX strategy at Exchange Bank of Canada in Toronto.
The euro firmed across the board, rising 0.6% against the dollar to $1.1737 <EUR=EBS>, after hitting a one-week peak. The single currency also climbed to a two-week high versus the yen, and was last 0.8% at 124.04 yen <EURJPY=EBS>.
European Central Bank policymakers are increasingly divided over how to steer Europe's economy through a second wave of COVID-19 infections.
The dollar fell to a one-week low against the Swiss franc and was last down 0.6% at 0.9194 franc <CHF=EBS>.
Markets were also waiting for developments in talks over aid for people affected by the coronavirus in the United States.
U.S. House Speaker Nancy Pelosi said on Tuesday she hoped to have a coronavirus aid deal with the White House this week, after speaking with Treasury Secretary Steve Mnuchin for about 50 minutes and making plans for further talks on Wednesday.
Sterling, meanwhile, rose on hopes for a Brexit deal and the Bank of England's deputy governor saying he thought the floor for the central bank's key interest rate was 0.1%.
The pound was last up 0.3% at $1.2867 <GBP=D3>.
Currency bid prices at 5:03PM (2103 GMT)
Description RIC Last U.S. Close Pct Change YTD Pct High Bid Low Bid
Euro/Dollar EUR= $1.1744 $1.1742 +0.02% +4.76% +1.1744 +1.1744
Dollar/Yen JPY= 105.6200 105.6400 -0.02% -2.98% +105.6200 +105.6500
Euro/Yen EURJPY= 124.01 124.05 -0.03% +1.69% +124.0600 +124.0500
Dollar/Swiss CHF= 0.9196 0.9192 +0.04% -4.98% +0.9196 +0.9198
Sterling/Dollar GBP= 1.2860 1.2861 -0.01% -3.01% +1.2862 +1.2857
Dollar/Canadian CAD= 1.3387 1.3387 +0.00% +3.09% +1.3391 +1.3388
Australian/Doll AUD= 0.7131 0.7127 +0.06% +1.57% +0.7131 +0.7126
Euro/Swiss EURCHF= 1.0799 1.0796 +0.03% -0.49% +1.0799 +1.0801
Euro/Sterling EURGBP= 0.9129 0.9127 +0.02% +7.98% +0.9130 +0.9130
NZ NZD= 0.6588 0.6586 +0.03% -2.20% +0.6588 +0.6590
Dollar/Norway NOK= 9.4187 9.4185 +0.00% +7.29% +9.4253 +9.4190
Euro/Norway EURNOK= 11.0630 11.0617 +0.01% +12.45% +11.0720 +11.0604
Dollar/Sweden SEK= 8.9278 8.9580 -0.16% -4.49% +8.9580 +8.9747
Euro/Sweden EURSEK= 10.5306 10.5306 -0.16% +0.59% +0.0000 +0.0000
(Reporting by Gertrude Chavez-Dreyfuss; Editing by Alistair Bell)
By Gertrude Chavez-Dreyfuss