Cardinal Wolsey (Orson Welles) summons Sir Thomas More (Paul Scofield) to his grand palace at Hampton Court. Wolsey seeks More's backing in his quest to secure a divorce from the Pope, enabling the King to marry Anne Boleyn. He expresses frustration at More being the lone voice of dissent in the Privy Council. Upon hearing More's insistence that the Pope will never grant such a divorce, Wolsey is taken aback by More's refusal to endorse his plan to exert "pressure" for an annulment. More stands firm, asserting that legal and religious avenues have been exhausted, leaving no basis for the Pope to approve such a request.
As More takes a ferry back to his estate along the River Thames, he encounters Richard Rich (John Hurt), a young acquaintance from his Cambridge days. Ambitious and drawn to power, Rich implores More for a position at Court. However, More, warning him of the rampant corruption within, suggests that Rich pursue a career in teaching instead.
Upon returning home, More discovers his daughter Meg (Susannah York) with William Roper (Corin Redgrave), a young Lutheran who seeks to marry her. More, a devout Catholic, firmly declines—"no" will be his answer as long as Roper remains a heretic.
Wolsey, stripped of his power and banished from Court after failing to manipulate the Pope into granting a divorce, meets his demise. Meanwhile, King Henry (Robert Shaw) promotes More to Lord Chancellor of England. Soon after, the King unexpectedly visits More at home on a barge to probe about the divorce. More, caught between his conscience and the King's expectations, stays resolute, even as Henry oscillates between veiled threats and enticing offers of royal favor. The King's temper flares when More refers to Catherine as "the Queen," leading to a fit of rage as he storms off, leaving his courtiers scrambling to keep up, much to his amusement.
At the riverbank, Rich encounters Thomas Cromwell (Leo McKern), who slyly suggests he might have information that could tarnish More's reputation in exchange for a position at Court. Meanwhile, Roper—having heard of More's discontent with the King—reveals a radical shift in his own beliefs, boldly declaring that the King has become "the Devil's minister" by challenging the Catholic Church. More, anxious for Roper’s safety, urges caution as Rich returns, once more seeking a Court position. When More denies him again, Rich spitefully claims that More's steward is a spy for Cromwell, unraveling an alarming truth for More and his family, including his wife Alice (Wendy Hiller)—that Rich is indeed being used by Cromwell.
Despite the pleas of his family to have Rich arrested for his treachery, More maintains his stance, insisting that Rich, while a threat, has broken no laws. As Rich aligns himself with Cromwell, their combined efforts intensify against More. Frustrated by the Vatican's inaction regarding his annulment, Henry declares himself the "Supreme Head of the Church in England," forcing both Parliament and the bishops to forsake their allegiances to the Pope. In quiet defiance, More resigns his chancellorship rather than submit to the new order, recognizing that the time has come for discretion over open discourse.
The King's demands escalate, compelling More to attend his wedding to Anne Boleyn. More, steadfast in his principles, resists and is summoned back to Hampton Court, now ruled by Cromwell, where he faces interrogation about his beliefs. Citing his rights under English law, More's refusal to respond only enrages Cromwell, who threatens him with charges of treason.
Returning home, More learns from Meg about a newly circulated oath regarding the marriage to Anne Boleyn. Initially, he contemplates taking the oath, conditional on it aligning with his conscience. However, understanding the implications—that the King cannot claim supremacy over the Church as that role is reserved for the Pope—More ultimately refuses to take the oath, leading to his imprisonment in the Tower of London.
Despite Cromwell's coercive tactics, the subtle influence of Archbishop Thomas Cranmer, and the entreaties of both Norfolk (Nigel Davenport) and his family, More remains unyielding in his principles. When brought to trial, he remains silent until convicted of treason, based solely on the perjured testimony of Richard Rich, who soon after receives a promotion to Attorney General for Wales as a reward.
Facing a grim fate, More boldly denounces the King's overreach, invoking the Biblical authority of the Papacy and the sanctity of the Church's immunity from State interference, as guaranteed by the Magna Carta and the King's own Coronation Oath. The courtroom erupts in chaos as spectators protest, yet More is condemned to die.
In the aftermath, a narrator recounts the fates of the principal figures: More's head is displayed on Traitor's Gate for a month until his daughter Margaret retrieves it, keeping it until her decease. Cromwell eventually faces execution for high treason within five years of More, the Archbishop is burned at the stake, and although the Duke of Norfolk narrowly escapes execution, his life ultimately hangs by the King's demise from syphilis. Meanwhile, Richard Rich climbs to the highest echelons of power as Chancellor of England, living out his days unscathed.
