She powered back from down the field in the last 150 metres to take fourth place in a time of 4.05.63 in the second of tonight's heats.
She now lines up in Monday's final alongside defending champion, world record holder and Olympic silver medallist Genzeba Dibabahas, who scraped through by the skin of her teeth, and fellow Brit Laura Muir. It will be her first World Championships final.
Laura, a former student at Alnwick's Duchess's Community High School and a Morpeth Harrier, said after the race: "I don't think I have run a race like that in my life. That last 150 metres I knew I had three or four people I had to catch and hold off. Down that home straight, I've never found myself in a position where I'm actually gaining places. I'm just so thrilled to make the final. That was so special."
The 26-year-old led the race from the gun, prompting BBC commentator Brendan Foster to say: "She looks confident, she looks strong."
But Konstanze Klosterhalfen, of Germany, moved to the front and, at the bell, had a 20-metre lead on the rest of the pack. Sifan Hassan led the pursuit and Klosterhalfen faded down the field.
On the home straight, Laura dug in and battled back, to the cheers of the home crowd in the London Stadium.
She said: "There's no greater feeling for me than competing in front of a home crowd. I love competing in this stadium. I can't wait for Monday.
"If I just keep believing in myself like I have all year and just enjoy the race, no matter what happens on Monday night I will be delighted with."
Laura's coach Steve Cram was full of praise for the brave run. "She's gutsy, gutsy, she's strong, strong. She loves hard races. She's found a little bit of extra pace this year. She will fight and fight right to the line."