Fontbona was born in 1942 and attended a Catholic high school. When she was a 17-year-old, she met Andrónico Luksic Abaroa who was 20 years older than she and married him by the time she was 18. Luksic had five children by his first wife, Patricia Lederer, who had predeceased him. Fontbona became the mother of Andrónico Luksic Craig when he was a 7-year-old. Another son was Guillermo Luksic, who died of lung cancer in 2013. The couple had three children of their own. One son, Davor Luksic, was mentioned as having several offshare companies in the Panama Papers.

Fontbona acquired her wealth following the death of her husband, Andrónico Luksic Abaroa, in 2005 from cancer.

Fontbona and her family control Antofagasta, the Santiago-based mining company. Through the publicly-traded company Quiñenco, they control Banco de Chile, Madeco, a copper products manufacturer, the country's largest brewer CCU, and a shipping company, CSAV. CSAV is the world's 16th largest shipping company as measured by TEUs. In 2013, she controlled 65% of Antofagasta.

In 2014, Forbes considered Iris Fontbona & family to be the 4th richest family in Latin America. She is the only woman to appear on Forbes list from Latin America. For several years, she was one of only two billionares in Chile on the list, before being joined by nine others in 2016. In 2015, she was ranked 82nd on the Forbes list. In 2013, Fontbona was ranked the 35th richest person on Bloomberg's Billionare List. This position fell to 83rd in 2016. Fontbana lost a quarter of her wealth in 2012.

In 2015, Fontbona donated a record $3,100 million CLP to the annual Chilean Telethon, which seeks to help children with physical disabilities. She appears on television for a telethon, which also takes place before a live audience.

In 2016, she donated another large sum, $4,400 million CLP, which assisted in setting a record for the charity event in terms of funds raised.