[1] In 1953, he began work on a method of natural family planning, involving observation of several indicators of fertility and infertility, gradually focusing on the changes to cervical mucus patterns of sensation.

[2] Although Billings maintained his career as a consulting neurologist to St Vincent's Hospital, he and his wife spent a large part of each year traveling to other countries, and training teachers in the Billings Ovulation Method, lecturing to doctors and students, and establishing teaching centers.

[1] The Method pioneered by the Billings was approved by both the Catholic Church and used by the World Health Organization.

[2] In 1969, John Billings was appointed a Knight Commander of the Order of St Gregory the Great (KCSG) by Pope Paul VI.

In 2003, Pope John Paul II added a star to this papal knighthood (KC*SG).