The Down runner was racing in Bern, Switzerland this evening where she set the new national record of 1.59.69.
The previous record was held by Rose Anne Galligan.
Mageean placed first in the final, beating Hedda Hynne from Norway and France's Renelle Lamote to the line.
This is Mageean's first competition in five months, on the day the opening ceremony for the Toyko 2020 Olympics, for which she had qualified, was due to be held.
