Avery was born in Halifax, Nova Scotia in 1877 to Francis Joseph Avery, a Baptist minister, and his wife Elizabeth Crowdy. The couple had immigrated from Britain in 1873. Oswald Avery was born and grew up in a small wooden row house on Moran Street in the North End of Halifax, now a designated heritage building. When Avery was 10, his family moved to the Lower East Side of New York City. Avery earned his undergraduate degree at Colgate University and was a member of the Class of 1900. Avery studied music at first and then switched to medicine at college, earning his medical degree and beginning a practice in 1904.

In 1912, Rufus Cole, who had noticed some of Avery’s publications, offered him a position at the recently opened Rockefeller Hospital, a facility for clinical research and part of the Rockefeller Institute. Avery accepted. At the institute, Cole, Avery and Alphonse Dochez developed the first effective immune serum against a strain of pneumococcus, a bacterium causing pneumonia. The serum was produced from the blood of infected horses.

At the height of the 1918 influenza epidemic, the dominant hypothesis was that the causative agent in the disease was a bacterium — specifically, Haemophilus influenzae (then called ‘Pfeiffer’s bacillus’ or Bacillus influenzae), a microbe first isolated by German bacteriologist Richard Pfeiffer, which he had identified in nasal samples of patients infected by seasonal influenza decades earlier and which was also found in many but not all samples taken from patients in the 1918 epidemic. The failure to isolate B. influenzae in some patients was generally attributed to the difficulty of culturing the bacterium.

For many years, genetic information was thought to be contained in cell protein. Continuing the research done by Frederick Griffith, Avery worked with Colin MacLeod and Maclyn McCarty on the mystery of inheritance. He had received emeritus status from the Rockefeller Institute in 1943, but continued working for five years, though by that time he was in his late sixties. Techniques were available to remove various organic compounds from bacteria, and if the remaining organic compounds were still able to cause R strain bacteria to transform then the substances removed could not be the carrier of genes. S-bacteria first had the large cellular structures removed. Then they were treated with protease enzymes, which removed the proteins from the cells before the remainder was placed with R strain bacteria. The R strain bacteria transformed, meaning that proteins did not carry the genes causing disease. Then the remnants of the S strain bacteria were treated with a deoxyribonuclease enzyme which removed the DNA. After this treatment, the R strain bacteria no longer transformed. This showed that DNA was the substance that transformed R strain into S strain bacteria and indicated that it was the carrier of genes in cells.

Nobel laureate Joshua Lederberg stated that Avery and his laboratory provided “the historical platform of modern DNA research” and “betokened the molecular revolution in genetics and biomedical science generally”. Avery is best known for his discovery in 1944, that DNA is the material of which genes and chromosomes are made.

Alfred Hershey and Martha Chase furthered Avery’s research in 1952 with the Hershey–Chase experiment. These experiments paved the way for Watson and Crick’s discovery of the helical structure of DNA, and thus the birth of modern genetics and molecular biology. Of this event, Avery wrote in a letter to his youngest brother Roy, a bacteriologist at the Vanderbilt School of Medicine: “It’s lots of fun to blow bubbles but it’s wiser to prick them yourself before someone else tries to.”