Catherine was a daughter of Sir Thomas Parr of Kendall, an official of the royal household. She had been widowed twice—in marriages to Edward Borough (died c. 1529) and to John Neville, Lord Latimer (died 1542 or 1543)—by the time she married Henry on July 12, 1543. Her tactfulness enabled her to exert a beneficial influence on the king during the last years of his reign. She developed close friendships with the three children Henry had by previous marriages and devoted herself to their education. A humanist, she was friendly with Protestant reformers. Timely access to the king saved her from conservatives, especially Stephen Gardiner (Gardiner, Stephen), who were bent on her destruction in 1546.

After Henry's death in January 1547 Catherine married a former suitor, Thomas, Lord Seymour of Sudeley, who was admiral of England from 1547 to 1549, but she died shortly after giving birth to a daughter. A learned and deeply religious woman, she wrote A Lamentacion or Complaynt of a Sinner in the last year of her life.