When she was 23, Marca Bristo, a nurse in Chicago, was sitting with a friend on the shore of Lake Michigan. Her friend’s dog accidentally knocked a prized pair of Ms. Bristo’s shoes into the water and, without a second thought, she dived in to retrieve them.

Striking her head, she broke her neck and was paralyzed from the chest down. In that instant, Ms. Bristo’s life changed forever in ways she could never have anticipated. She lost her job, her health insurance, could no longer use public transportation and had no access to many public places.

But rather than dwell on her misfortune, she became a powerful advocate for people with disabilities, spending her life working to change perceptions and the rules in a world that had traditionally ignored the needs of the disabled. She was a key player in the passage of the Americans With Disabilities Act of 1990, which outlawed discrimination against the nearly 50 million Americans with disabilities.

After a long battle with cancer, Ms. Bristo died on Sunday at 66 in her home in Chicago. Her death was confirmed by her husband, J. Robert Kettlewell.