Liam Hanley, of no fixed address and unemployed, was found guilty of grievous bodily harm with intent by a jury at Lewes Crown Court today.
The court heard that Hanley stabbed his former partner Sarah Harries in the bath at her flat on Shoreham Beach last September.
The 32-year-old was charged with attempted murder and his trial began on February 25.
After two and a half week trial, a jury found him guilty of grievous bodily harm with intent. He has been remanded in custody and will be sentenced on May 10.
After the verdict was returned, Detective Constable Katy Lewis said: "This was a horrific attack on a woman which came completely out of the blue, shocking Sarah herself and the close community in Shoreham.
"There was no history of violence from Liam and Sarah was truly shocked by ferocious nature of the attack.
"Sarah has thankfully made a recovery however the scars and some of her injuries will have an impact on her for the rest of her life.
"She has bravely taken to the stand during the trial and faced Liam once again; I commend her for this and so grateful she is here to do so."
On Tuesday, September 4, Hanley and Sarah, 37, who had been in an on-off relationship for around a year, had spent the day together in Shoreham where Sarah lived, a police spokesman said.
While piecing together the events of the day, officers traced CCTV which showed the couple together in the town.
They had visited Lidl to buy food and went to McDonalds for lunch.
At 6pm, the couple went to the Ferry Inn pub in East Street for a drink, said police.
They then went to Co-op to buy some tobacco.
When they returned home, Sarah ran herself a bath and got in - however a short time time later Hanley came into the bathroom and began stabbing her, police said.
Sarah managed to get out of the bath and fought him off, and during the fight they moved from the bathroom to the kitchen before Hanley left the flat, police said.
Desperate Sarah made an urgent call to emergency services pleading with them to hurry to get to her quickly,.
Emergency services rushed to her aid and found the flat covered in blood and Sarah crouched on the floor in the hallway, said police.
A spokesman said: "Sarah had suffered stab wounds to her neck, abdomen and arms with the deepest wound to her neck.
"She suffered a punctured lung.
"She was taken to Royal Sussex County Hospital where she underwent emergency surgery. Miraculously Sarah survived her horrific injuries."
Hunt for Hanley
In the meantime the hunt was on by police to trace her partner, Hanley.
An image was issued to try and find him and officers began an extensive search, police said.
On leaving the flat Hanley had called a friend in Lancing who, unaware of what had happened, arranged for a lift with another friend to take Liam to Slough in Berkshire, police said.
During the journey Liam asked to stop for a cigarette and dumped a bag of clothes at the side of the road, according to police.
The driver dropped him off and while returning home received an alert from the Sussex Police's Facebook page alerting Hanley was wanted.
The driver immediately returned to Liam's friend, who had already called the police and waited for officers there to give them details about what had happened, police said.
The next day, after staying at another friend’s house, Liam called police and handed himself into police in Maidenhead.