Four-month-old Lily Aitken died at home in Spondon, Derbyshire after sleeping in the seat for an extended amount of time.
Derby and South Derbyshire Coroner's Court heard that the baby was found in a lifeless condition by her mum and dad, Luke Aitken and Emma Buckby in April.
They heard that the little girl often slept in the seat as she would not settle in her Moses basket and liked, according to her mum - to be 'squashed up' in her car seat.
The inquest was told that Lily had slept overnight in the seat, waking at six am for a feed and change. She then went back to sleep in the seat until midday, where again she was fed and changed and went back to sleep. Her parents checked on her at 2.45pm and found her lifeless.
The emergency services attempted to resuscitate her, but she was pronounced dead shortly after arriving at hospital.
Andrew Wright, from Derbyshire Police, who led the investigation into the baby's death told the court:
"There was no question of suspicious circumstances surrounding Lily's death. She was a well cared for, healthy little girl. There was nothing out of the ordinary surrounding her care. Social services were involved with the family and there were no concerns."
Paediatric pathologist Dr Mudher Al-Adnani carried out the post-mortem on Lily and found nothing to explain her death.
"The only thing I noticed what that Lily was small for her age, but I knew that she was premature so this is not unusual," he said, "She was fully developed and was in good health. She seemed to be a normal four-month-old baby."
As Lily was not in her cot or Moses basket at the time of her passing, Dr Al-Adnani said that he could not conclude that she died of cot death.
He said: "The medical advice is that babies are not to be left to sleep in their car seats for a long period of time.
"We do not know if being in her car seat was anything to do with Lily's death. It could just be a coincidence and this could have happened anyway."
Louise Pinder, the deputy coroner returned a narrative verdict and said that Lily died of sudden infant death syndrome due to natural causes:
"Nothing in the post-mortem examination could explain Lily's death. Lily died as a result of sudden infant death syndrome but because of potentially unsafe sleeping circumstances," she said.
Such a sad story. How many of us have left babies in car seats and bouncers?