Her storming finish provided jockey Kieran Shoemark with a first Group One success, while it was a first at the highest level for Jarvis since Grand Lodge won the St James's Palace Stakes in 1994.
Owned by music agent Emma Banks - who said pre-race she felt like she was headlining Glastonbury - the five-year-old hit the front just over a furlong out and powered away from there.
For a mare having her first run over 10 furlongs Shoemark was in no doubt about the 100/30 winner's ability to see out the trip - and rather than play his hand late he kept things simple and the result was never in doubt.
Viewed as an unlucky loser in the Falmouth Stakes last time out - the form of which was franked in the Sussex Stakes by Alcohol Free and Snow Lantern - Lady Bowthorpe was in third before careering away from Zeyaadah and Joan Of Arc.
Zeyaadah was a length and a half behind at the line, with Joan Of Arc another half-length back. Breeders' Cup winner Audarya briefly threatened, but her challenge proved short lived as she faded into fifth.
Newmarket-based Jarvis said: "It's fantastic, we've dreamt about this for a long time, we knew she was special.
"I'm so chuffed for the team at home more than anything else, they've worked incredibly hard, we only have a staff of seven or eight.
"They all just work so hard for Lady Bowthorpe, it's all due to them.
"I was confident she'd stay, I was a little bit worried about Roger's (Varian) filly (Zeyaadah), she wasn't stopping, but I knew we've got that great turn of foot - that's her real strength.
"She's relaxed, she's settling so much better now, she's a superstar. She's not had the luck, she's had to come back and she has.
"She's a very, very special mare to train and she's owned by a delightful owner, she gives me free rein though of course we discuss things - she's superb."
He added of Shoemark, who was handed a six-month riding ban in November 2018 and has spoken frankly since about the addiction problems that led to his suspension: "I'm absolutely delighted for Keiran, he's a delightful young man, he's got impeccable manners, he went to a bad place but he's come out the other end.
"He's great, he's a lovely guy to work with."
Shoemark, 25, said: "I'm pretty speechless. This means so much, not just for me but for Emma and William Jarvis, too. I feel very lucky to be part of it.
"She deserves it - she's done nothing but improve with age and she's a credit to Emma, who fills me with absolute confidence.
"I know the filly so well and I can tell what form she is in cantering to the start. She was taking a bit of a hold with me and I knew she was in good form, and she appreciates a bit of give in the ground.
"I know it was her first run over 10 furlongs, but she'd been finishing over a mile really well - her last furlong had been her best furlong - and I wasn't concerned about that. I knew when we hit the front it was going to a good one to pass us."
On battling back from his problems, he said: "I always believed if I got myself clean and sober I could get myself back on track and to where I wanted to be.
"That was the thing that was holding me back - thankfully I'm here. I've won a Group One today, but I'm already looking forward to the next one."
Banks said: "Kieran gave Lady Bowthorpe an amazing ride. He deserves this, it is his first Group One - it's a first Group One for all of us apart from William who had one back when the dinosaurs were doing it.
"It's fantastic. I was sitting next to Luca Cumani who half a furlong out looked at me and said 'you've got this'. If Luca Cumani says that then you know you've got it.
"I'm so proud of Lady Bowthorpe. I'm proud of Kieran who had a lot of pressure and he has had some bad luck on her and today we won.
"I pay the bills, that's all I do really. William is a fantastic trainer, he has lots of my horses. They are not all as good as this one unfortunately."
Connections of Zeyaadah were equally thrilled with her effort - and gracious in defeat.
Shadwell racing manager Angus Gold said: "Our filly has turned into a star and moved beautifully, but in truth I've never been as happy to finish second.
"It was a fabulous run from Zeyaadah - if you'd told me a year ago she would win a Listed and finish second in a Group One I would have found it hard to believe it. She just has a really good mind and loves it."