Cundy was born in Cedar Falls, Black Hawk County, Iowa, USA, on 16 July 1911, as the last of four children born to parents Jens (James) Larsen Markussen (1867–1949) and Elizabeth Lauritsen (1880–1977). Her father was born in Denmark, and her mother was born in Iowa to Danish parents. She had three older siblings: Annetta McBride (1903–1981), Eva Magrethe Markussen (1906–1907), and Edward Markussen (1908–1979). She graduated from Cedar Falls High School in 1928.
On 2 November 1949, she married John E. Cundy (1914–1976). The couple had no children. She was employed at Northwestern Bell Telephone Company from 1930 until her retirement in 1975, holding the position of District Traffic Chief Clerk in Waterloo.
Cundy passed away in Cedar Falls, Black Hawk County, Iowa, USA, on 29 October 2021, at the age of 110 years, 105 days.
At the time of death, she was the second-oldest living person in the U.S. state of Iowa, behind Hazel Young.
Her age was validated by LongeviQuest on 12 September 2023.
* “Margaret Elizabeth Markussen Cundy” – Find A Grave
* “Margaret Elizabeth Cundy Obituary” – Richardson Funeral Service