Shepherd, 30, who also fell into the water after the incident in December 2015, survived but on Thursday, July 26, he was convicted of manslaughter by gross negligence.
Shepherd has gone on the run after skipping bail and was being tried in absentia.
The jury heard he bought the speedboat "to pull women."
After meeting the 24-year-old on dating website OkCupid, he took her for a meal at The Shard — London's tallest building, with impressive views over the city — and then drove the speedboat past the Houses of Parliament.
The pair had drunk two bottles of wine between them and the boat capsized near Wandsworth Bridge and she was hurled into the water.
Her body was recovered half an hour later but she could not be resuscitated.
The trial heard the 75-horsepower vessel, which had been moored next to Shepherd's houseboat in Hammersmith, had a number of defects.
Speedboat owner Jack Shepherd has been convicted of manslaughter after his date died when she took the wheel on the Thames, hit a log and was thrown with him into the water— CourtNewsUK (@CourtNewsUK) 26 July 2018
The jury also heard the speed limit on that stretch of the Thames was 12 knots but Shepherd had been doing 29.9 knots.
The boat — a red Fletcher Arrowflyte GTO — was produced as an exhibit in the car park of the Old Bailey courthouse for the jury to examine during the unique trial.
Shepherd had not offered Miss Brown a lifejacket and they were still tucked away at the front of the boat.
Port authority surveyor Andrew Thomas, who compiled a report on the speedboat, said the kill cord on the boat was poorly maintained and had no attachment.
Jack Shepherd has been found guilty of killing Charlotte Brown, 23, while on their first date. He took her out on the Thames in his speedboat but they fell into the water when it hit some branches https://t.co/6lorHomEs4. PHOTO: The recovered speedboat pic.twitter.com/guqEhQgY4m— CPS (@cpsuk) 26 July 2018
He also said the steering wheel had a "degree of play", giving it a "good deal of wobble backwards and forwards".
"Although Shepherd had been drinking excessively he knew what he was doing and was desperate to show off his speedboat in a vain attempt to impress young women. He waited for the highest tide to enable faster speeds. He brazenly offered over the controls of his defective vessel to a woman who had no previous experience with boats. To do this at night, whilst drinking and driving erratically in winter conditions without offering the passenger a life jacket or asking if they could swim was a recipe for disaster. Sadly it did end in tragedy for Charli. Our thoughts are with her family at this difficult time," said Detective Sergeant Christopher Davies.
He said the police were appealing for help from the public in tracing Shepherd, who was last seen in March 2018 in his home city of Exeter in the west of England.