Britain is about to get its first Catholic prime minister in more than 500 years. No Roman Catholic has occupied the role of chief minister to the English crown since the 1550s, when Queen Mary I attempted to reverse the English Reformation that had begun during the reign of her father, Henry VIII. That is set to change with the elevation of Andy Burnham on July 20.

In the centuries that followed Mary’s death, English Catholics had their freedom of worship and general civil rights heavily restricted. There is still on the statute books a law that declares that those who “professe the Popish Religion” are not allowed “to inherit possess or enjoy the Crown and Government of this Realm.” England remains specifically defined as a Protestant nation even though public officeholders are no longer required to take an oath rejecting the doctrine of transubstantiation.

Previous prime ministers have therefore, unsurprisingly, exercised caution regarding Catholicism. Tony Blair regularly attended Mass with his Catholic wife and children, but waited until he left Downing Street before being received into the church. A more recent prime minister, Boris Johnson, though he was baptized a Catholic in infancy, was confirmed as an Anglican at school at Eton and led a notoriously irreligious life before exploiting a technicality in canon law to marry his third wife in Westminster Cathedral.

By contrast Mr. Burnham—who now takes over from Keir Starmer, an avowed nonbeliever—was born and raised a Catholic and has sent his three children to a Catholic school. As a member of the House of Commons he has not always voted in line with church teaching on issues such as same-sex marriage and abortion. Indeed, he has repeatedly criticized the church’s “austere and judgmental” record on gay rights and in 2015 urged Pope Francis to “bring the church into the 21st century” on same-sex marriage. 

But his politics are nuanced. Though he has voted against tightening abortion laws, he irritated progressives in 2008 by unsuccessfully voting to preserve the legal requirement that in vitro fertilization clinics consider the “need for a father,” which had made it more difficult for lesbian couples to access I.V.F. services. And he questioned the Assisted Dying Bill brought before the Commons last year, though not explicitly on pro-life principles: Instead, he said he could not support it while hospices were so underfunded.

Mr. Burnham is certainly not a cradle Catholic who has left his faith behind, as some have suggested. Last month, when he took his oath as he re-entered Parliament, he chose to swear on the Jerusalem Bible, the widely used translation popular among Catholic members of Parliament taking the oath in the House of Commons. 

He is said to be an occasional Mass-goer and has described himself as “not particularly religious.” The family are Catholics but, he says, borrowing a Scouse phrase of his mother’s, “we don’t lick the altar steps.” Scouse is the colloquial term to describe the culture of Liverpool, the English city to which millions of Irish Catholics emigrated in the 19th and 20th centuries. Today some 75 percent of the area’s population have some Irish ancestry, and the city remains culturally entwined with the Catholic faith. Most significantly, Britain’s new prime minister insisted in 2015: “Catholic social teaching underpins my politics.” 

Young Burnham was schooled in this teaching from early on. As an altar boy he fought with his brothers to secure the coveted job of holding the paten beneath the chins of those receiving holy communion. But one of his other duties made a greater long-term impression. He had to supervise the playing of the homilies of the archbishop of Liverpool, Derek Worlock, which were recorded on tape and sent out to local parishes on particular Sundays. 

This was the era in which Margaret Thatcher’s economic revolution was taking a devastating toll on working-class communities as heavy industry was closed down across the north of England. She locked horns with the National Union of Mineworkers in the most bitter dispute in U.K. industrial history. Archbishop Worlock, who had been present at all the sessions of the Second Vatican Council, was an advocate of the social gospel: “I can pray for [my neighbor’s] soul,” he once said, “but I cannot turn my back on how he is to live: his wellbeing, his freedom, his prosperity or poverty, his house, his job and so on.” 

Conservatives in the Westminster government decided the archbishop was a dangerous radical—a verdict many in the Vatican already shared because of his previous calls for Pope Paul VI to relax the edict against contraception for married couples. He and the Anglican bishop of Liverpool, David Sheppard, together played a key role in bridging the city’s divides, strengthening social trust and championing the flourishing of local communities. The two bishops wrote a book called Better Together: Christian Partnership in a Hurt City and grew so ecumenically close that they were said to have undone the Reformation in a single city. 

Archbishop Worlock made a massive impression on the young Andy Burnham. The vast majority of the teachers at Burnham’s Catholic school saw the political embodiment of his social gospel in Britain’s Labour party. “There was, and still is,” said Mr. Burnham, “a direct read-across between what I was learning at school and church and Labour values.”

A passionate soccer fan, Mr. Burnham supports Everton F.C., which has existed under the perennial shadow of the city’s more successful team, Liverpool. One of the politician’s favorite tropes was to say that three institutions had shaped him: Everton Football Club, the Labour Party and the Catholic Church. “In that order,” he would joke. More seriously, he once added: “I’ve always felt that there’s a connection between the three in terms of identity and that’s about the underdog, a sense of solidarity, and values.”

The political commentator most plugged into Mr. Burnham’s circle, Patrick Maguire of the London Times, says that the papal encyclical that best speaks to Mr. Burnham’s relationship with his faith is Pope Leo XIII’s “Rerum Novarum,” which in 1891 established the basis of Catholic social teaching with its insistence on balancing the rights of workers and the rights and responsibilities of an increasingly overweening capitalist class. But Mr. Burnham’s politics, Mr. Maguire says, grow from experience and not theological abstraction.

Last month his first keynote speech as prime minister-in-waiting was filled with echoes of Catholic social teaching, particularly respect for human dignity and the importance of balancing solidarity and subsidiarity in pursuit of the common good.

Mr. Burnham set out a program of economic regeneration and re-industrialization, with a major “rebalancing of power” shifting a key part of the Downing Street operation from London to Manchester, the northern city of which he was until recently mayor—and where economic growth has been double that of the rest of the U.K. under his watch. Manchester is to become the new political node for the spread of economic revitalisation to other neglected regions.

His proposal for a huge transfer of power away from Westminster is not simply a managerial reform. It restores agency to the politically marginalized in line with the Catholic insistence that every person, being made in the image of God, has inherent dignity. It embodies the insight of the pastoral constitution of Vatican II, “Gaudium et Spes,” with its insistence that political institutions exist for people, not vice versa. As with Pope John Paul II’s “Centesimus Annus,” it specifically links human dignity with participation in social and political life. And it reiterates Pope Francis’s insistence in “Fratelli Tutti” that no people or region should be treated as disposable or “left behind” by economic or political systems. 

Mr. Burnham’s pledge to build more houses for the poor than at any time in the last 50 years acknowledges another basic requirement of human dignity. So does his plan to reduce the government welfare bill “in a way that is fair and lasting”—in contrast to the botched attempts of the Starmer government. His determination that vocational education should enjoy equal esteem with the academic resonates strongly with “Laborem Exercens,” where Pope John Paul II declares that the dignity of work derives from the dignity of the individual working man or woman, rather than from their social status or economic productivity. 

Moving key government decision-making out of London is classic subsidiarity, the antidote to the temptation for the state to take over tasks which can be done just as well at a lower level—a temptation Pope Pius XI condemns in “Quadragesimo Anno” as a “a grave evil.” Mr. Burnham’s assertion that “growth cannot be ordered from the top down [but] only be nurtured from the bottom up” is a secular expression of this. 

The other great pillar of Catholic social teaching alongside subsidiarity is solidarity. This is, asserts Pope John Paul II in “Sollicitudo Rei Socialis,” “not a feeling of vague compassion or shallow distress at the misfortunes” of others but “on the contrary…a firm and persevering determination to commit oneself to…the common good”—another key concept in Catholic social teaching. This undergirds Mr. Burnham’s desire for economic “growth in every postcode and hope in every heart” and for a less adversarial politics.

And his promise of “greater public control of essential services”—water, energy, housing and transport—echoes one of the most consistent papal themes. Leo XIII, Pius XI, John XXIII, John Paul II, Benedict XVI and Francis all endorsed the free market, with varying degrees of enthusiasm, but all insisted that “the right ordering of economic life “cannot be left to a free competition of forces” and that “government must intervene when justice requires it.” The current pope, Leo XIV, has declared that “the economy and enterprise can and must be engines of inclusion, and of justice.”

Andy Burnham is a far more charismatic politician than the outgoing British prime minister. He speaks the language of the living room. He will eschew theological language much as he does ideological. His vocabulary is moral, framing politics in terms of fairness, dignity and belonging. But its roots are clear.