The device, used to give a high-energy electric shock to the heart in the event of a cardiac arrest, was supplied by Henry Boot Construction, the contractor for The Glass Works.
The defibrillator, installed at the right-hand side of the May Day Green entrance to the market, can be used without training, and adds to existing devices already installed at the town hall and at the Alhambra.
Coun Jim Andrews, cabinet spokesman for public health, said: “We’d like to thank Henry Boot for supplying the defibrillator at the market.
“It’s a vital piece of equipment that could potentially save lives.
“Defibrillators need to be available in busy areas where crowds gather or somewhere that an ambulance may take time to reach due to traffic congestion, so the market is an ideal location.”
Ryan O’Loughlin, director, Henry Boot Construction Limited, said: “We are delighted to be able to provide this potentially life-saving equipment for Barnsley Market.
“Having worked closely with the markets team and traders for the past two years, this joint initiative extends our collaboration and continues our support for the local community.”