Cullingworth was born in Leeds, and worked there for his father's business before deciding to take up medicine. He trained as an apprentice at Leeds School of Medicine, qualifying as MRCS in 1865, and LSA a year later. He worked as a resident at MRI before entering private practice. Experienced in a number of areas, Cullingworth worked as a police surgeon and lectured in medical jurisprudence at Owens College Manchester. He published papers on medico-legal questions and on atrophy. In 1881 he was awarded an MD from Durham University. Increasingly, Cullingworth specialised in obstetrics and gynaecology, he was surgeon at St Mary's Hospital Manchester from 1873 and was appointed professor of obstetric medicine at Owens College in 1885.
Cullingworth was an active member of the Manchester Medical Society , serving as both its honorary secretary and librarian. He did much important work in the latter post; he also catalogued the Radford Library at St Mary's. In 1888 he moved to London to become senior obstetric physician at St Thomas's Hospital. He published many of his most important papers on obstetrics and gynaecology, in Transactions of the Obstetrical Society of London, including those on peritonitis, ovarian fibroma, and disease of uterine appendages.