He graduated MB BS at the University of London in 1887 and joined Leeds General Infirmary as a house surgeon.

In 1935, a year before his death, Moynihan and Dr Killick Millard had founded the British Voluntary Euthanasia Society.

[2] Moynihan's surgery on Park Square, Leeds in the city centre still stands, now used as private offices.

[6] There is a lecture theatre/conference space at Thackray Medical Museum, Leeds, named the "Moynihan Auditorium".

Lord Moynihan died six days later at the age of 70 and was succeeded in the barony and baronetcy by his only son Patrick.