Yellen -- who is expected to become the new head of the Fed in early 2014 -- will appear before the Senate Banking Committee at 10 a.m. ET.
Her prepared remarks to the committee, released late Wednesday, show that she intends to encourage growth by maintaining accommodative monetary policies.
"Part of the rally we saw yesterday (and this morning) was partly driven by relief that Yellen is not about to take on a substantially less-dovish tone in today's testimony in an effort to garner the support of the more hawkish elements of the Senate Banking Committee," wrote Deutsche Bank analyst Jim Reid in a market report.
The comments gave market participants hope that Yellen would continue the Fed's current $85-billion-per-month bond-buying program for the next few months. The program -- also known as quantitative easing or 'QE' -- has helped spur stocks by pumping markets with extra cash.
Asian markets ended the day with gains. A weaker yen helped Japan's Nikkei jump 2.1%. The currency eased after official figures showed the country's economy grew 1.9% in the third quarter - a sharp slowdown from the previous quarter.