The Dawson's Creek actress and the popstar appear in the movie - an adaptation of Lois Lowry's dystopian novel - alongside Odeya Rush, Meryl Streep and Jeff Bridges, which opens in US cinemas on Friday 15 August.
But back to their elegant outfits - did someone say matching?
Swift, 24, pulled out all the stops in a Monique Lhuillier gown with red structured top and nude pink skirt, Casadei heels and blingy Brumani earrings. The siren red lipstick and side-swept down hair do? Pure glamour.
Holmes, 35, played up her signature understated style in a beautiful pink pleated Zac Posen dress, grey heels and sparkly Lorraine Schwartz jewels.
Clearly the ladies talked through co-ordinating colours ahead of the premiere, as did Odeya Rush and Meryl Streep who both did red applique at last night's sparkly soiree.
There is nothing worse than a red carpet clash situation, though it rarely happens when the line-up is this good.
If only Katie had done the red lipstick thing or carried a scarlet clutch to give her look that edge.
LOVE KATIE HOLMES' HOLLYWOOD GLAMOUR? Click through this style evolution to see more looks from the American actress.
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