Cecile Klein was born in Montreal, Quebec, Canada on 15 June 1907, the second of five children born to parents Louis Efros (1881–1950) and Rebecca Pearson (1887–1965), who were Jewish immigrants from what is now Poland. According to her family, one of her great-grandmothers lived to the age of 103. During the Spanish Flu pandemic of 1918, Klein and her father would make door-to-door visits to neighbors to check on sufferers of the disease, delivering home-cooked meals that her mother had made.

In the early 1920s, she began attending secretarial school at the age of 15, despite the age requirement for entry being 16. She taught herself how to write in shorthand from reading books she took home, and would practice by taking notes while listening to radio news reports. Because she didn’t have a typewriter at home, she was able to practice typing by drawing a keyboard using a dime to trace the keys, and writing the letters by hand. Upon graduating, she found work at a lawyer’s office, before becoming employed by RCA Victor.

In 1932, she married a pharmacist named Erwin Klein (1905-1999), who was born in present-day Israel, and would go on to have three children with him. She helped her husband run his pharmaceutical company, International Drugs, by doing administrative work. During World War II, they manufactured and delivered medicine to hospitals throughout Montreal. The couple loved traveling, and would frequently visit countries until Erwin’s death in 1999 at the age of 94.

At the age of 95, she bought a new watch, and made the optimistic choice to pay for a 10 year warranty, insisting that she would live to 105 and beyond. She was a lifelong learner, and enjoyed taking courses and attending lectures on law, medicine, and science. She was passionate about theater, and later became a devotee of the Côte St. Luc Dramatic Society, always attending their musical productions. Throughout her centenarian years, the group would celebrate her birthdays with special performances. At the age of 103, she fell and broke her hip, and was told by doctors that she would never walk again, but she managed to regain all of her mobility after attending physical therapy.

Up until the age of 110, she lived in the same home she first moved into in 1948, until a hip fracture in 2017 forced her to move into a nursing home. From that point on, she was no longer able to walk and required more assistance from caregivers. As a supercentenarian, she still had most of her teeth, and could read the newspaper without glasses. At the time of her 114th birthday in 2021, she had become less verbal and was unable to be interviewed, but still moved to the music being played for her.

Cecile Klein died in Cote Saint-Luc, Quebec, Canada, at the age of 114 years, 212 days. She was survived by three children, eight grandchildren, 18 great-grandchildren and five great-great-grandchildren.