Worn by: Jamie Dornan as Christian Grey
Reference: Omega Speedmaster
Brand: Omega
In both the book and the movie there are Omega watches. The main character Christian Grey (played by Jamie Dornan) wears the 44.25mm Speedmaster Co-Axial in gold, with reference 311.63.44.51.01.001. Other Omegas in this movie are the Aqua Terra and the Aqua Terra Chronograph with a white dial.
Source: https://www.fratellowatches.com/speedmaster-in-movies/