Jodi Jaecks, 47, who had surgery to remove both breasts last year, had argued that wearing a bathing suit covering her chest caused searing pain, Reuters reported.
After two surgeries, chemotherapy and the mastectomy in March 2011, Jaecks said she wanted to swim to regain her strength.
She had been asking for permission to swim topless at Seattle's Medgar Evers pool since February, but staff had said no, the Seattle Times reported.
According to city spokesperson Dewey Potter, quoted by Reuters, a sign at the pool stated: "This is a family recreation facility. Please dress and act accordingly."
Other city employees at the pool said there was an unwritten city policy that required "gender-appropriate" bathing suits, Jaecks told Reuters.
But this week, acting Seattle Parks and Recreation Superintendent Christopher Williams told Jaecks she would be granted an exception to swim topless at all public pools during adult lap swim times.
And Williams, who according to the Times is himself fighting cancer, also phoned Jaecks her to apologize.
"I'm very sensitive to what this woman is going through," Williams reportedly said.
"On one hand our staff was just fulfilling their duties; but at some point, you have to back away from the policy and use common sense."
"It was not a policy change, but only an exception for me," Jaecks said, the Associated Press reported.