Gerald Mellin, 54, tied one end of a rope to a tree, then climbed into his open-top Aston Martin DB7 with the other end around his neck.
He then accelerated into one of Swansea's main roads and met his grisly end as other drivers watched in horror.
An eye-witness told the inquest hearing Thursday how the Aston Martin passed her just after midnight on Mumbles Road on September 14.
Alison Anniah said: "It got my attention because it was going so slowly.
"As the car passed us I saw the body had no head."
Officers found his headless body still on the leather driving seat of the car with his head on the back seat.
The court was also told that shortly before his death Mellin had cancelled his life insurance policy.
He had also taunted his estranged wife Mirrielle, 33, by showing her the rope in the boot of his Ģ90,000 car.
Mother-of-two Mirrielle told the inquest: "We had split up and been to court.
"He wanted me to walk away from the farmhouse and the business and leave me with nothing.
"We met in a pub after a court hearing and he started having a tantrum.
"As we made our way back to our cars he opened the boot and said: 'There's my rope, that's what I'm going to kill myself with'. I told him to grow up and give me the rope. But he just laughed."
Swansea Coroner's Court heard that she and Mellin had been in court the day before his death, where she was awarded an extra Ģ100 a week from him to help with the running of her house.
Mellin had been staying at various hotels in the Swansea area after moving out of the family home, WalesOnline reported.
Mrs Mellin said that on the fateful evening she received a text from him saying: "Congratulations XXX". It was the last time she heard from him.
Mellin owned a gym and sun tanning centre called Bodytalk and his wife worked there as a beautician.
Mirrielle said Mellin had self-harmed and made several attempts on his life during their short and "horrendous" marriage, but she always believed it was "a cry for help" rather than a real attempt at suicide.
She also said she did not know about the financial pressure he was under until after his death when she discovered he was in "an extortionate amount of debt".
The inquest in Swansea heard that after her husband's death she discovered he had cancelled a life insurance policy which would have paid out to her.
She said: "He ran up an extortionate amount of debt. I've got to sell the farmhouse now, just to pay the debts.
"Gerald created the debt because he always said if I left him, he would leave me with nothing."
Detective Constable Ceri John said records showed Mellin was being treated for depression at the time of his death and was first seen by a psychiatrist at the age of four for anxiety.