The SpiceJet plane was flying from Bangalore to Delhi in India when the foul odour became unbearable.
See also: British Airways flight diverted over 'smelly poo in toilet'
See also: Strange smell forces BA flight to Greece to return to Gatwick
Passengers noticed the smell just a few minutes into the flight and it got so bad that the pilots - who were also overcome by the odour - decided to divert to the nearest airport.
The Boeing 737, carrying nearly 200 crew and passengers, including four infants, landed safely in Hyderabad so the odour could be investigated.
The bizarre flight diversion occurred on Sunday morning after the smell was reported in the plane's front lavatory, near the cockpit.
A spokesperson for the budget airline - whose tagline is "Red, Hot, Spicy" - described it as a "very foul smell".
The cause of the odour was not revealed.
After flight SG192 landed in Hyderabad the plane was cleaned and ventilated before being returned to service around three hours later.
Passengers eventually continued their journey to Delhi, which normally takes around two hours to complete, following the delay.
A SpiceJet spokesman told reporters: "SpiceJet B-737 operatingSG192 had to be diverted to Hyderabad due to very foul smell from forward lavatory coming into the cockpit.
"After landing in Hyderabad, the lavatory and cockpit were thoroughly cleaned and ventilated before the aircraft was released for service."
It's not the first time a commercial aircraft has been forced to divert due to a foul smell coming from a toilet.
In March 2015 a British Airways flight from London to Dubai was forced to return to Heathrow due to an unbearable odour.
The pilot told travellers that the smell was due to "liquid faecal excrement", a passenger revealed.