structural:expansion, quality:corruption
Married life and medical career

Grace was married on 9 October 1873 to Agnes Nicholls Day (1853–1930), who was the daughter of his first cousin William Day. Two weeks later, they began their honeymoon by taking ship to Australia for Grace's 1873–74 tour. They returned from the tour in May 1874 with Agnes six months pregnant. Their eldest son William Gilbert junior (1874–1905) was born on 6 July. Grace had to catch up with his studies at Bristol Medical School, and he and his wife and son lived at Downend until February 1875 with his mother, brother Fred and sister Fanny.

The Graces moved to London in February 1875, when W. G. was assigned to St Bartholomew's Hospital, and lived at Earl's Court, about five miles from the City. Their second son Henry Edgar (1876–1937) was born in London in July 1876. A ward in the Queen Elizabeth II Wing at St. Bartholomew's Hospital used to bear the name "W. G. Grace Ward", caring for patients recovering from neurosurgery until demolition of the Queen Elizabeth II building. In the autumn of 1877, the family moved back to Gloucestershire, where they lived with Grace's elder brother Henry, who was a general practitioner. Grace's studies had reached a crucial point with a theoretical backlog to catch up followed by his final practical session. Agnes became pregnant again at this time and their third child Bessie (1878–98) was born in May 1878.

Following the 1878 season, Grace was assigned to Westminster Hospital Medical School for his final year of medical practice and this curtailed his cricket for a time as he did not play in the 1879 season until June. The family moved back to London and lived at Acton. But the upheaval was worthwhile because, in November 1879, Grace finally received his diploma from the University of Edinburgh, having qualified as a Licentiate of the Royal College of Physicians (LRCP) and became a Member of the Royal College of Surgeons (MRCS). After qualifying he worked both in his own practice at Thrissle Lodge, 61 Stapleton Road in Easton, a largely poor district of Bristol, employing two locums during the cricket season. He was the local Public Vaccinator and had additional duties as the Medical Officer to the Barton Regis Union, which involved tending patients in the workhouse.

There are many testimonies from his patients that he was a good doctor, for example: "Poor families knew that they did not need to worry about calling him in, as the bills would never arrive". The family lived at four different addresses close to the practice over the next twenty years and their fourth and last child Charles Butler (1882–1938) was born.

After leaving Gloucestershire in 1900, the Graces lived in Mottingham, a south-east London suburb, not far from the Crystal Palace where he played for London County, or from Eltham, where he played club cricket in his sixties. A blue plaque marks their residence, Fairmount, in Mottingham Lane.