Glenys Kinnock, a former European lawmaker and British government minister who helped secure for women a central role in the continent’s politics, died on Dec. 3 at her home in London. She was 79.

Her family confirmed the death, saying she was diagnosed with Alzheimer’s disease in 2017.

Her death was the first in a political dynasty built around her husband, Neil Kinnock, who led Britain’s Labour Party beginning in 1983, and a son, Stephen Kinnock, a Labour lawmaker, both of whom survive her, along with a daughter, Rachel Kinnock, a onetime Labour Party campaigner who became a television producer.

For many years Glenys Kinnock was seen primarily as the companion of her husband in his ill-starred efforts to reform the Labour Party and return it to power after the unbroken Conservative ascendancy of Margaret Thatcher and John Major between 1979 and 1997.

Notably, she was at Mr. Kinnock’s side in 1983 when, during a photo-shoot on the pebbles of Brighton Beach in southern England, he stumbled into the incoming tide. That image of haplessness continued to haunt him in his unsuccessful campaigns to take over as prime minister — a dream that ended in 1992, when he lost national elections and quit as Labour Party leader. The party was returned to power only with the landslide election victory of Tony Blair in 1997.

Mr. Kinnock’s departure from British parliamentary jousting was significant for Ms. Kinnock, who resolved to launch her own bid for a political career by running for a seat in the European Parliament, representing part of Wales, in 1994, when Britain, before Brexit, was still part of the bloc.

She broke the news about her decision to seek office while she and her husband were driving.

“I nearly drove off the road,” Mr. Kinnock was quoted as saying in Martin Westlake’s “Kinnock: The Biography” (2001). The decision, he said, meant that she could act “as if her first obligation was to herself, for the first time in her life.”

She won the seat.

By then she had already staked out her own political identity, one generally viewed as further to the left than her husband’s. For instance, at a time when he was seeking to distance Labour from its traditional commitment to unilateral nuclear disarmament, she was actively supporting the idea.

In 1983, Ms. Kinnock had visited with women who were picketing an American air base at Greenham Common in southern England to press demands for the removal of American cruise missiles. She also supported militant miners who were on strike in the mid-1980s to protest government plans to close collieries.

A year after she joined the European Parliament, her husband was appointed a high executive official of the European Union, and the Kinnocks became known as a power couple in Brussels, the bloc’s headquarters.

Throughout their careers they withstood Conservative jibes that she was a scheming backstage power. The accusation rankled her. “It was relentless, the description of me as being very manipulative and always undermining Neil,” she was quoted as saying.

The perception endured. Even the left-leaning newspaper The Daily Mirror noted in her obituary, “As Labour’s dynamic duo the Kinnocks were nicknamed ‘the Power and the Glory’ — and everyone knew exactly who was the Power: Glenys.”

Glenys Elizabeth Parry was born on July 7, 1944, in Roade, a village in the English Midlands, to Cyril and Elizabeth (Pritchard) Parry. Her father was a railway signalman and a Labour Party activist. She once recalled that he took her along as an infant while electoral canvassing, piling pamphlets in her carriage.

In her childhood, the family moved to Holyhead, on the island of Anglesey in North Wales. As a teenager, she became a Labour Party member and an active campaigner against nuclear weapons. She studied education and history at University College, Cardiff, where she met her future husband, then worked as a teacher. They married in 1967 and had been together for 56 years at her death.

Ms. Kinnock served for 15 years as a socialist member of the European Parliament, specializing in international development. In Britain, newspapers supporting the Conservatives took to accusing the Kinnocks of living a charmed life, enjoying the perquisites associated with a so-called European Union gravy train.

In 2005, her husband was appointed to the British House of Lords as Lord Kinnock, a title that theoretically permitted Ms. Kinnock to style herself Lady Kinnock, but she declined to adopt the honorific, the BBC reported.

In 2009, Gordon Brown, Britain’s prime minister at the time, appointed her as a junior government minister. Under British rules, only lawmakers in either the lower or upper house of Parliament are permitted to be government ministers. So Mr. Brown ennobled her as Baroness Kinnock of Holyhead, providing her with a seat in the House of Lords, the upper chamber. She took over responsibilities for Britain’s relations with Europe and then with Africa, until Labour lost the 2010 election.

Ms. Kinnock resigned from the House of Lords in 2021, four years after her Alzheimer’s diagnosis.

“We can’t imagine what that day was like for her,” her children Rachel and Stephen wrote in The Times of London in 2022. “She never complained, but we know that she was terrified. For such a formidable, strong, intelligent, funny and dignified woman, to feel her mind slipping away must have been devastating.”