Emergency services were called to the brewery at 12.30pm on Wednesday, following reports of an ammonia leak. The victim is believed to be in his 40s.
One man has been left in a “serious, but stable condition”, while 11 staff, two police officers and nine firefighters were taken to hospital, according to the emergency services.
Production at the site has stopped temporarily while the investigation takes place, Carlsberg has confirmed.
Carlsberg UK chief executive officer Julian Momen, said: “We are deeply, deeply saddened by this tragic incident and subsequent fatality.
“Our immediate thoughts are with the individual’s family, friends and colleagues at this very difficult time and we will support them in every way we can.
“Our further thoughts and support are with our colleagues and members of the emergency services who are being treated in hospital.
“One of our colleagues remains in a serious, but stable condition. Nothing is more important to us than the safety of everyone working for us.”
The beer giant is working with the authorities to investigate how the “tragic incident occurred”, he added.
“We will be in a position to say more once a full investigation has been concluded.”
Northamptonshire Police confirmed staff from the brewery, along with emergency service workers, had been treated in hospital.
The force was now working with the Health & Safety Executive to “investigate the incident”, it added.