The 23-year-old took the water on the final day of competition in France as the fastest qualifier, looking to reclaim the title she won three years ago in Istanbul.
And despite qualifying fastest Miley had plenty left in the tank for the final, touching home in 4:23.47 for victory, beating the previous European best of 4:24.21 set by Spain's Mireia Belmonte Garcia.
This gold medal added to the 800m freestyle and 200m medley silvers Miley had already won to ensure she left France with an impressive haul.
Miley was joined on the podium by Hungarians Katinka Hosszu and Zsuzsanna Jakabos in second and third respectively, with fellow Brit Aimee Willmott swimming a personal best 4:32.56 to finish fourth.
Craig Benson, in his first senior international final, set a personal best of 2:07.02 to finish sixth in the men's 200m breaststroke.
The gold went to Russian Vyacheslav in 2:04.55, with Ukrainian duo Igor Borysik and Andriy Kovalenko taking silver and bronze respectively.
And it was a similar story for Karley Mann in the 200m backstroke as she marked her first senior international final with a sixth-place finish, clocking 2:06.16, the gold going to Ukrainian Daryna Zevina.
The other Brit in action was Antony James who despite improving his 50m butterfly heat time to 23:53 seconds in his semi-final, failed to reach the final, which was won by Spain's Rafael Munoz Perez.
There was another European record in Chatres on the final day as Dane Rikke Moeller Pedersen touched home in 1:04.12 to claim gold in the women's 100m breaststroke.
Camille Muffat could not repeat her 400m freestyle world record pace in the 200m final but she still came away with the gold medal.
The men's 100m individual medley title was won by Russian Vladimir Morozov in 51.80 seconds, with Ilaria Bianchi taking the women's 100m butterfly gold.
France's Yannick Agnel took the men's 200m freestyle title and his compatriot Jeremy Stravius claimed victory in the 100m backstroke.
Belarus' Aliaksandra Herasimenia took the final individual gold in the women's 50m freestyle before France and Denmark picked up the men's 4x50m freestyle and women's 4x50m medley relay titles respectively.