Boffins say the eight minute track, called Weightless, is so effective at inducing sleep it should not be listened to while driving.
Carefully arranged harmonies, rhythms and bass lines help to slow the heart rate, reduce blood pressure and lower levels of the stress hormone cortisol.
Manchester trio Marconi Union worked with sound therapists to create the soothing tune, which also slows breathing and reduces brain activity.
Scientists played the song to 40 women and found it to be more effective at helping them relax than songs by Enya, Mozart and Coldplay.
The study - commissioned by bubble bath and shower gel firm Radox Spa - found the song was even more relaxing than a massage, walk or cup of tea.
The women were connected to sensors and given challenging puzzles to complete against the clock in order to induce a level of stress.
They were then played different songs as their heart rate, blood pressure, breathing and brain activity were recorded.
Studies found Weightless was 11 per cent more relaxing than any other song and even made many of the women "drowsy" in the lab.
It induced a 65 per cent reduction in overall anxiety and brought them to a level 35 per cent lower than their usual resting rates.
The song features guitar, piano and electronic samples of natural soundscapes.
It is pierced throughout by buddhist-like chants that induce a trance-like state.
Lyz Cooper, founder of the British Academy of Sound Therapy, said Marconi Union had used scientific theory to make the "perfect relaxing song".
She said: "The song makes use of many musical principles that have been shown to individually have a calming effect.
"By combining these elements in the way Marconi Union have has created the perfect relaxing song.
"The study found this to be the world's most relaxing song.
"It contains a sustaining rhythm that starts at 60 beats per minute and gradually slows to around 50.
"While listening, your heart rate gradually comes to match that beat.
"It is important that the song is eight minutes long because it takes about five minutes for this process, known as entrainment, to occur.
"The fall in heart rate also leads to a fall in blood pressure.
"The harmonic intervals - or gaps between notes - have been chosen to create a feeling of euphoria and comfort.
"And there is no repeating melody, which allows your brain to completely switch off because you are no longer trying to predict what is coming next.
"Instead, there are random chimes, which helps to induce a deeper sense of relaxation.
"The final element is the low, whooshing sounds and hums that are like buddhist chants.
"High tones stimulate but these low tones put you in a trance-like state."
She added: "Sound therapy has been used for thousands of years to help people relax and improve health and well-being.
"Music was at the heart of healing and worship among indigenous cultures.
"Anybody who lives under a flight path or near a busy road appreciate the effect sounds can have on your stress levels.
"Weightless is ideal for putting on at the end of a stressful day and unwinding."
Dr David Lewis-Hodgson, from Mindlab International, which conducted the research, said: "The results clearly show that the track induced the greatest relaxation - higher than any of the other music tested.
"Brain imaging studies have shown that music works at a very deep level within the brain, stimulating not only those regions responsible for processing sound but also ones associated with emotions.
"In fact, Weightless was so effective, many women became drowsy and I would advise against driving while listening to the song because it could be dangerous."
Richard Talbot, from Marconi Union, said: "It was fascinating working with a therapist to learn how and why certain sounds affect people's mood.
"I always knew the power of music but we have previously written using gut feeling."
Cassie Shuttlewood, from Radox Spa, said: "Most of us feel stressed every day but Radox understands that it's not necessary to spend hundreds of pounds on massages, spa weekends and yoga retreats in order to relax."