Williams is in her 18th Grand Slam final; Radwanska in her first.
The 30-year-old American defeated Radwanska in their only two matches, one of them in the Wimbledon quarterfinals four years ago.
Williams topped Belarusian Victoria Azarenka 6-3, 7-6 (8-6) and Radwanska beat German Angelique Kerber 6-3, 6-4 in Thursday's semifinals.
Radwanska, who has been bothered by a respiratory illness at Wimbledon, is the first Polish finalist in a Grand Slam event in 73 years.
Williams has won three WTA titles this year and 41 in her career.
She and her sister, Venus, have combined to win nine of the last 12 Wimbledon championships. Serena won the event in 2002, 2003, 2009 and 2010.
The 23-year-old Radwanska is bidding for her 11th WTA title. She also has won three events this year.
The winner will collect $1.8 million.