Margaret Nelson was born on March 12, 1973, in San Francisco, California, United States. She is a daughter of Bruce Arthur Nelson, a lawyer, and Barbara Jo Nelson, maiden name Mixer, a business writer and consultant. She was the second child. When Margaret was seven, her mother fell in love with a man who'd painted the Nelson house. Her parents divorced the following year, and after that Margaret and her sister Emily split their time between their father's place and the home their mother shared with her new husband.