The Scottish actor, who plays Podrick Payne in the cult fantasy series, spoke of his support for the referendum campaign ahead of the Empire magazine awards, celebrating global talent across film and television genres.
He told reporters: “If I could run the British empire for a day I would give Scotland its independence.
“I am absolutely for it with the kind of mess we are in now.”
The 25-year-old tweeted about his passion for an independent Scotland amid heightened discussion over the possibility of a second referendum in the country during the last week.
“I am very vocal about it,” he added. “But everybody is entitled to their own opinion.”
As Game Of Thrones comes towards its eighth and final series, after the seventh airs this summer, he said he was “sad” to be reaching the end of an era of his career, but described it as an “amazing experience”.
Commenting also on his interest in the James Bond films, he added that he would love to see Idris Elba cast as the next 007 because “I think a black Bond is where things should go now”.
Portman joined guests including Sir Patrick Stewart and Tom Hiddleston on the red carpet at the event in north London’s Roundhouse, marking the end of this year’s major film awards season.
Felicity Jones has been tipped for best actress following her role in Rogue One: A Star Wars story, while Eddie Redmayne and Benedict Cumberbatch are in the running for best actor.