Benjamin Disraeli’s Jewishness has been a problem for his biographers, especially his English biographers. Robert Blake’s classic study (1966) — still the hallmark account of Disraeli’s political career — makes little of his boastful celebrations, on the floor of the House of Commons and in the pages of his novels, of the Jews and their contributions to civilization. For Blake and other English historians, Disraeli’s over-the-top embrace of his Jewishness is a distraction, better sidelined than explored.

Not so for Adam Kirsch. His new biography, “Benjamin Disraeli” (Schocken Books, 260 pages, $21), foregrounds Disraeli’s sense of his own Jewish identity, along with the obstacles this posed to his career, and makes it the key to understanding his behavior. Disraeli’s father, Isaac, a well-liked figure in literary circles in late-Georgian England, had his children baptized in 1817, when Benjamin was 12. His motive was entirely strategic: He wanted to ease his children’s way in the world. A follower of Voltaire and the radical enlightenment, Isaac Disraeli had no use for revealed religion, whether Jewish or Christian, and there was nothing out of the ordinary in his decision: Well-to-do, religiously unobservant Sephardim in England at this time routinely left the Jewish fold, through conversion, intermarriage, and disaffiliation from the synagogue in Bevis Marks.

As a newly minted Anglican, the younger Disraeli was in a better position to make his way in the world than he would have been if he had remained nominally Jewish. Various Christological oaths still barred Jews from playing an active role in public life (as opposed to commercial and financial life). But conversion was not the panacea that Isaac Disraeli might have hoped it would be. Both friends and foes alike continued to see his son’s Jewishness, his ethnicity, as an essential, even determinative, part of his character, a part that remained behind even after baptism.

Moreover, Benjamin Disraeli looked “un-English.” His luxuriant curls, Mediterranean complexion, and “intensely black eyes” made him feel different. The eponymous hero of his novel “Contarini Fleming” (1832), one of his many fictional characters who give voice his innermost feelings, remarks that there was “no similitude” between him and those around him. “Their blue eyes, their flaxen hair, and their white visages claimed no kindred with my Venetian countenance. Wherever I moved I looked around me, and beheld a race different from myself.” As Mr. Kirsch explains, Disraeli’s own fiction (he wrote 18 novels over the course of his accomplished life) abounds with ambitious young men, convinced of their genius, who feel that they are strangers.

From the time that Disraeli entered public life, standing unsuccessfully for a seat in Parliament in 1832, his opponents made the most of his Jewishness. At election meetings, he was taunted with cries of “Shylock!” and “Old Clothes” (a reference to the low-status secondhand clothing trade in which Jews were prominent) and offers of ham and bacon. Cartoonists in Punch and other illustrated magazines regularly depicted him as a Jewish old-clothes seller. At the end of his career, in 1876, when Turkish soldiers massacred Bulgarian Christians, destabilizing the Balkans and making the fate of the Ottoman Empire once again a focus of European diplomacy, liberals attacked him for pursuing a “Semitic” policy when he reasserted Britain’s traditional support for maintaining the crumbling empire’s integrity.

What was a talented, determined young man of Jewish birth to do? Disraeli could have ignored the taunts, flaunted his Christian credentials, and labored to distance himself from his family’s past, as was so common at the time. The path he chose, Mr. Kirsch convincingly explains, was in fact the opposite: to reject the stigmatized identity that English culture and society saddled him with, and “to reimagine his Jewishness as a glorious inheritance.” Mr. Kirsch’s explanation of how Disraeli did this takes note of both the sympathetic and the repellent dimensions of the chauvinism he embraced. Disraeli’s imagination transformed the Jews into the linchpin of European civilization: They were the true aristocrats, the only people to whom God ever spoke directly (that is, revealed himself), already civilized when Europeans were still “tattooed savages.” Not only were they talented and creative, but they were powerful as well, exercising enormous influence behind the scenes. (Disraeli’s descriptions of Jewish power, which he puts into the mouth of Sidonia, a mysterious character in his political novels of the mid-1840s, creepily foreshadow the ranting of anti-Semites later in the century.) What Disraeli was doing was creating a countermyth of Jewish superiority, one that would turn contemporary, unflattering views of Jews on their head. It was a countermyth that also allowed him to mock, and thus take revenge on, the English aristocracy and gentry, whose snubs and slights he suffered.

For Disraeli to lay claim to being a Jew, however, he needed to redefine the term, for he was no longer theologically a Jew but a Christian. He did so by replacing the bonds of belief and practice with the bonds of race. Disraeli was, in his own view, as Jewish as his friend Lionel de Rothschild, for they both belonged to the same race. As Sidonia declares in “Coningsby,” “Race is everything; there is no other truth.” Moreover, like other racial thinkers, Disraeli associated racial purity (and the refusal to intermarry and absorb outsiders that protected it) with power, vigor, and survival. The Jews were “an unmixed race of a first-rate organization.” In the aftermath of the Holocaust, views like these are disturbing, to say the least, but it is to Mr. Kirsch’s merit that while acknowledging the troubling elements of this approach, he is able to set out the historical and emotional circumstances that led Disraeli to it. While not willing to accept Disraeli’s racial premises, he understands the task they performed for him and thus what made them attractive to him.

Mr. Kirsch is the not the first to take Disraeli’s Jewish mythmaking seriously, and to explore what it did for him. Hannah Arendt and Isaiah Berlin, both outsiders to English political culture, wrote in a similar vein decades earlier. But Mr. Kirsch is the first to explore at length how these ideas functioned not only imaginatively but also politically, suggesting concrete ways in which Disraeli’s mythmaking informed his conduct of politics, especially his relations with the Tory notables whom he led in Parliament. This is the most speculative part of his book, but also the most original. Historians of British politics may balk, but Mr. Kirsch’s Disraeli is a more human, more complex, and more sympathetic figure than the one they conventionally present.

Mr. Endelman is the William Haber Professor of Modern Jewish History at the University of Michigan, and the author of “The Jews of Georgian England, 1714-1830,” “Radical Assimilation in Anglo-Jewish History, 1656-1945,” and “The Jews of Britain, 1656-2000.”