The 23-year-old already has two silver medals to her name in France but looks well placed to go one better in the 400m IM after winning her heat by almost seven seconds.
And Miley's time of 4:31.34 minutes was the quickest across all four heats, with Hungarian Katinka Hosszu - who already has three gold medals to her name - 1.78 seconds behind.
Aimee Willmott lowered her personal best to 4:33.29 minutes to join Miley in the final as the fourth-fastest qualifier; however Sophie Smith and Lucy Spencer missed out after finishing 17th and 19th respectively.
Miley kicked things off on Sunday by posting a personal best 26.22 seconds in the women's 50m freestyle, but it wasn't enough to qualify for the semi-final.
And it was a similar story for Marco Loughran in the men's 50m butterfly as his personal best time of 24.16 seconds was some way off forcing him into the semi-final.
However compatriot Antony James has a slim hope of swimming again as his time of 23.67 seconds put him 18th overall and first reserve.
One Brit who will definitely feature in a final is Craig Benson after he knocked more than two seconds off his 200m breaststroke personal best to win his heat in 2:07.99 minutes and qualify him as sixth fastest for his first senior international final.
Lewis Coleman also set a new personal best as he touched home in 2:13.87 minutes to finish 27th.
Karley Mann became the fourth Brit to qualify for a final as she set a new personal best of 2:05.88 minutes to progress as the fourth fastest qualifier.
Lauren Quigley, Willmott and Smith tried to join her, the former setting a new personal best of 2:09.54 minutes, but just missed out.
Both Siobhan-Marie O'Connor and Molly Renshaw set new personal bests in their 200m freestyle heats but it wasn't enough to make the final as they finished 11th and 36th respectively.
And it was a similar story in the men's 200m freestyle as Calum Jarvis, Joseph Patching and Coleman all set personal bests - the latter's second of the morning - but they miss out on the final.
Coleman, Jarvis, James and Loughran then joined forced for the 4x50m freestyle and just missed out on the final as they finished ninth, two places better than the team of Quigley, Miley, O'Connor and Smith managed in their 4x50m medley.
- Sports & Recreation
- Sophie Smith