Noel Thomas has also worked with the same crewmate for 30 years, which is thought to be a record.
His retirement was made extra special as December 24 is also his birthday.
Mr Thomas said: “I thoroughly enjoyed my job. Retiring is either the best decision I've ever made, or the worst.
“My head and body are saying it's a wise decision but my heart is saying different.”
Delivered dozens of babies
Mr Thomas, who lives with his wife Christine, has two sons and has also fostered many children over the years.
He has also helped delivered dozens of babies during his career as a paramedic.
Mr Thomas added: “Certain jobs you see are horrific and will stay with you forever, but when we resuscitate someone or a patient says 'thank you', that's a feeling money cannot buy.
“In four days as a paramedic, you can bring in a life and be there when someone goes; it's like a circle.”
Crewmate or 30 years
Mr Thomas said his crewmate Christine Money – now retired herself – is one of the main reasons he stayed and enjoyed the job for so long.
He said: “Having a good crewmate makes this the easiest job in the world. It's like having a friend and you support each other, both in what's going on in your life and through the difficult jobs we have to attend.”
Mr Thomas started his career at Park Royal ambulance station September 6, 1976 and moved to Willesden ambulance station before he spend a majority of his career working from Wembley ambulance station.
He also said the most important part of the job was treating all people equally – rich, poor and everyone in between.
Assistant director of operations for London Ambulance Service , Ian Johns, said: “A forty year career serving London is an extraordinary milestone and the London Ambulance Service wishes Noel the very best in his retirement.”
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