Necker was born in the republic of Geneva (later incorporated with Switzerland in 1815). His father was a native of Küstrin in Neumark (Prussia, now Kostrzyn nad Odrą, Poland), and had, after the publication of some works on international law, been elected as professor of public law at Geneva, of which he became a citizen. Jacques Necker was sent to Paris in 1747 to become a clerk in the bank of Isaac Vernet, a friend of his father. By 1762 he was a partner and by 1765, through successful speculations, had become a very wealthy man. He soon afterwards established, with another Genevese, the famous bank of Thellusson, Necker et Cie. Peter Thellusson (otherwise known as Pierre Thellusson) superintended the bank in London (his son was made a peer as Baron Rendlesham), while Necker was managing partner in Paris. Both partners became very rich by loans to the treasury and speculations in grain.

In 1763 Necker fell in love with Madame de Verménou, the widow of a French officer. But while on a visit to Geneva, Madame de Verménou met Suzanne Curchod, who was the daughter of a pastor near Lausanne and who had been engaged to Edward Gibbon. In 1764 Madame de Verménou brought Suzanne to Paris as her companion. There Necker, transferring his love from the widow to the poor Swiss girl, married Suzanne before the end of the year. On April 22, 1766 they had a daughter, Anne Louise Germaine Necker, who became a renowned author under the name of Madame de Staël.

Madame Necker encouraged her husband to try to find himself a public position. He accordingly became a syndic or director of the  French East India Company, around which a fierce political debate revolved in the 1760s, between the company's directors and shareholders and the royal ministry over the administration and the company's autonomy. "The ministry, concerned with the financial stability of the company, employed the abbé Morellet to shift the debate from the rights of the shareholders to the advantages of commercial liberty over the company’s privileged trading monopoly."  After showing his financial ability in its management, Necker defended the Company's autonomy in an able memoir against the attacks of André Morellet in 1769.

Meanwhile he had made loans to the French government, and was appointed resident at Paris by the republic of Geneva. Madame Necker entertained the leaders of the political, financial and literary worlds of Paris, and her Friday salon became as greatly frequented as the Mondays of Mme Geoffrin, or the Tuesdays of Mme Helvétius. In 1773 Necker won the prize of the Académie Française for a defense of state corporatism framed as a eulogy of Louis XIV's minister, Colbert; in 1775 he published his Essai sur la législation et le commerce des grains, in which he attacked the free-trade policy of Turgot. His wife now believed he could get into office as a great financier, and made him give up his share in the bank, which he transferred to his brother Louis.

In October 1776 Necker was made director-general of the finances -- he could not be controller because of his Protestant faith. He gained popularity in regulating the finances by attempting to divide the taille or poll tax more equally, by abolishing the vingtième d' industrie, and establishing monts de piété (establishments for loaning money on security). His greatest financial measures were his usage of loans to help fund the French debt and his usage of high interest rates rather than raising taxes. He also advocated loans to finance French involvement in the American Revolution.

In 1781 France was suffering financially, and since Necker was Director-General, he was blamed for the rather high debt accrued from the American Revolution. While at court, Necker had made many enemies because of his reforming policies. Marie-Antoinette was his most formidable enemy, and she and his other enemies had a great influence over Louis XVI's decision to dismiss Necker in 1781. Also in 1781 Necker published his most influential work: the Compte rendu au roi. In the Compte rendu Necker summarizes governmental income and expenditures, giving the first-ever public record of royal finances. It was meant to be an educational piece for the people, and in it he expressed his desire to create a well-informed, interested populace. Before, the people had never considered governmental income and expenditure to be their concern, but now armed with the Compte rendu, they became more proactive. This birth of public opinion and interest plays an important role in the French Revolution. The statistics given in the Compte rendu were completely false and misleading, as Necker wanted to show France in a strong financial position when the reality was much worse. He "cooked the books", hiding the crippling interest payments that France had to make on its massive £520 million in loans (largely used to finance the war in America) as normal expenditure. When he was criticized by his enemies for the Compte rendu he made public his 'Financial Summary for the King', which appeared to show that France had fought the war in America, paid no new taxes and still had a massive credit of £10 million of revenue.

In retirement he occupied himself with literature, producing his famous Traité de l'administration des finances de la France (1784). He also spent time with his only child, his beloved daughter, who in 1786 married the ambassador of Sweden and became Madame de Staël. In 1787 Necker was banished by the lettre de cachet 40 leagues from Paris for his very public exchange of pamphlets and memoirs attacking his successor as minister of finance, Calonne. Yet in 1788 the country had been struck by both economic and financial crises, and Necker was called back to the office of Director-General of Finance to stop the deficit and to save France from financial ruin.

Necker was seen as the savior of France while the country stood on the brink of ruin, but his actions could not stop the French Revolution. Necker put a stop to the rebellion in the Dauphiné by legalizing its assembly, and then set to work to arrange for the summons of the Estates-General of 1789. He advocated doubling the representation of the Third Estate to satisfy the people. But he failed to address the matter of voting — rather than voting by head count, which is what the people wanted, voting remained as one vote for each estate. Also, his address at the Estates-General was terribly miscalculated: it lasted for hours, and while those present expected a reforming policy to save the nation, he gave them financial data. This approach had serious repercussions on Necker's reputation; he appeared to consider the Estates-General to be a facility designed to help the administration rather than to reform government.

Necker's dismissal on 11 July 1789 made the people of France incredibly angry, which induced the king to recall him. He was received with joy in every city he traversed, but in Paris he again proved to be no statesman. Believing that he could save France alone, he refused to act with Mirabeau or Lafayette. He caused the king's acceptance of the suspensive veto, by which he sacrificed his chief prerogative in September, and destroyed all chance of a strong executive by contriving the decree of November 7, by which the ministry might not be chosen from the assembly. Financially he proved equally incapable for a time of crisis, and could not understand the need of such extreme measures as the establishment of assignats in order to keep the country quiet. Necker stayed in office until 1790, but his efforts to keep the financial situation afloat were ineffective. His popularity had vanished, and he resigned with a broken reputation.

Not without difficulty he reached Coppet Commugny, near Geneva, an estate he had bought in 1784. Here he occupied himself with literature, but Madame Necker pined for her Paris salon and died soon after. He continued to live on at Coppet, under the care of his daughter, Madame de Staël, and his niece, Madame Necker de Saussure. But his time was past and his books had no political influence. A momentary excitement was caused by the advance of the French armies in 1798, when he burnt most of his political papers. He died at Coppet on April 9, 1804.

His daughter was to become a prominent figure in her own right and a leading opponent of Napoleon Bonaparte.