But getting into character wasn't exactly easy for the 32-year-old "Les Misérables" and "My Week With Marilyn" actor.
Redmayne spent four months studying Hawking’s life, which he recently explained to Variety was "a process that required so much research, it was like writing a doctoral dissertation."
Since the role called for Redmayne to portray the now 72-year-old Hawking at different ages of his life and stages of his motor neurone disease, the actor watched every single documentary and YouTube video he could find on the man.
“I tried to read literally everything I could get my hands on,” Redmayne told Variety. “It became hilarious, because I would get 40 pages in, and I was like — ‘Eddie, none of these words make any sense to you.’ ” So the actor began to work with a physics teacher at Imperial College London who was able to explain things more simply.
Redmayne also worked with a choreographer, Alexandra Reynolds, for four hours a day. “We put what we knew into picking up a pen, drinking, walking, existing,” Reynolds told Variety, adding that she would film the young actor on an iPad and they would then study the footage.
To better understand Hawking's paralyzing motor neuron disease, Redmayne visited a neurology clinic in London every two weeks, where he spoke with over 30 patients.
Redmayne compiled his findings on a sheet of paper he carried with him everywhere during shooting. “It was like the Magna Carta,” the film’s director, James Marsh, told Variety. “It became the most important document beyond the script.
Redmayne's physical transformation became more intense when he played Hawking during the later years of his life.
Marsh said that Redmayne was "really suffering, but he never complained" when he was forced to sit in a wheelchair for hours with his legs crossed and his head tipped over, in a position that made it harder for him to breathe.
Large prosthetic ears were used to make Redmayne appear smaller and older.
"When we wanted to get him thinner and smaller, do you know what we did?” revealed screenwriter Anthony McCarten. “You make the ears bigger and the whole body seems smaller.”
Redmayne took every detail seriously, down to his fingernails.
"I learned when he [Hawking] was 21 he decided to grow his nails as an act of defiance," Redmayne told E! Online, adding that he kept his nails long throughout filming despite "only one shot in the film where you see the nails."
Ultimately, the intense mental and physical preparations paid off for Redmayne.
After Hawking first screened the movie, he was moved to tears.
"The Theory of Everything" hits theaters November 7th. Watch the trailer below:
Read Variety's full interview with Eddie Redmayne here >