Sally Rooney has told the High Court she is "and will continue to be a committed supporter" of Palestine Action, which failed to secure a temporary block on it being banned as a terrorist group on Friday.
The Irish author said in court documents that the ban would prevent her from speaking at future public events as she "could not in good conscience disguise or lie about my principles" if it comes into effect at 12.01am on Saturday as planned.
If the ban does come into effect, it would make membership of, or support for, Palestine Action a criminal offence punishable by up to 14 years in prison.
I am and will continue to be a committed supporter of Palestine Action
Rooney has provided support for a legal claim by Huda Ammori, the co-founder of Palestine Action, against the Home Office, over the decision to proscribe the group under the Terrorism Act 2000.
Ms Ammori asked a High Court judge on Friday to temporarily block the move from becoming law over the weekend, ahead of a bid to be given the green light to challenge the Government's decision later this month.
But in a ruling, Mr Justice Chamberlain refused to block the ban, stating that any harm caused is "insufficient to outweigh the strong public interest in maintaining the order in force".
Barristers for Ms Ammori are seeking to appeal against the ruling on Friday evening.
In her witness statement, cited in Mr Justice Chamberlain's judgment, Rooney said the "cultural effects" of Palestine Action becoming proscribed "could not be easily mended".
She said: "Though I am based in Ireland, my work is published in the UK. My novels regularly appear in bestseller lists, and I often travel to Britain to speak in public about my work.
"I am and will continue to be a committed supporter of Palestine Action.
"If... that support is criminalised, I will effectively be prevented from speaking at any future public events in the UK, since I could not in good conscience disguise or lie about my principles in public.
"For any public figure to be labelled a 'supporter of terrorism' by the state would have serious consequences. It would likely end or severely restrict the careers of many emerging artists."
"If I continue to voice support for Palestine Action from my home in Ireland, what are the likely consequences? Will I be denounced publicly by the Prime Minister?
"Will bookshops go on stocking the work of an author the Home Secretary has branded a 'terrorist' simply for supporting a protest group?
"The BBC has adapted two of my books for television; both series are presently promoted on the iPlayer service. Normal People, which I co-wrote and produced, was the BBC's most-streamed series in 2020, with over 62 million views.
"My beliefs have not changed since the making of that series, and I have done nothing but continue to express them.
"If the expression of those beliefs becomes a terror offence under UK law, would the BBC continue to screen and promote my work?
"Is it likely that I could ever again collaborate with British public institutions like the BBC as I have done in the past?
"The cultural effects of proscription could not be easily mended, even if the Home Secretary later changed her mind.
"For any public figure to be labelled a 'supporter of terrorism' by the state would have serious consequences.
"It would likely end or severely restrict the careers of many emerging artists.
"'Terrorism' is not a trivial word."
In written submissions for Friday's hearing, Raza Husain KC, for Ms Ammori, said that Rooney "will continue to voice her support from Ireland" for the group.
He said: "Given her public support for Palestine Action... she is concerned that being labelled a 'supporter of terrorism' would have serious impacts on her ability to collaborate and publicise her work."
He continued: "Ms Rooney notes that 'countless artists, writers and members of the public support direct action against complicity in what Israel is doing in Palestine', including Juliet Stevenson, Paul Weller, Tilda Swinton, Brian Eno, and other signatories to an open letter dated 30 June 2025."
If Palestine Action loses its bid to temporarily block the move, it is due to become a terrorist organisation on Saturday after the order was signed by Home Secretary Yvette Cooper (PA)
Ms Cooper announced plans to proscribe the direct action group last month after two Voyager planes were damaged at RAF Brize Norton in Oxfordshire on June 20—an action claimed by Palestine Action.