Berger was born as Nils Berger in Sør-Odal, a municipality in the county of Innlandet, Norway, on 20 October 1885 to Hans Thorvald Nilsen and Karen Thorsdatter Aulimyren, who lived to be 99 and 81 respectively. He attended school until he was 13, and was fascinated by the United States, reading about the country frequently.
In June 1905, aged 19, Berger emigrated to the United States, moving in with an uncle in Minnesota. He spent time in several locations, including Rugby, North Dakota, as well as Montana and Saskatchewan, Canada. By 1910, he had started a livery business with a friend in the town of Springbrook.
That year, Berger homesteaded 12 miles from Springbrook, and married Tilla Melland, the daughter of Norwegian immigrants, in 1911. They had three children: Norma in 1912, Thelma in 1914, and Harold in 1916. They also adopted Melland’s nephew, Lester Stensaker, after the deaths of his parents in the 1920s.
Berger’s first car was a 1916 Ford Model T, and he bought his first radio in 1923. He worked as a farmer, doing so until his retirement in 1960, aged 75. He was widowed in 1985, after his wife’s death at the age of 90. The couple were married for 74 years.
Berger lived independently until the age of 104, when his eldest daughter moved in with him. He moved into a nursing home in Williston, North Dakota in 1992, aged 107. He died on 22 September 1996 at the age of 110 years, 338 days. He was among the top five oldest known men in the world upon his death.