Lamb was born in London in 1779. Educated at Eton and Cambridge University, he fell in with a group of Romantic Radicals that also included Percy Bysse Shelley and Lord Byron. In 1805 he married an acquaintance, Lady Caroline Ponsonby, and was elected to the House of Commons as the Whig MP for Leominster.
He first came to general notice for reasons he would rather avoided: his wife had a public affair with Lord Byron -- she coined the famous characterization of him as "mad, bad, and dangerous to know". The resulting scandal was the talk of Britain in 1812. Eventually the two reconciled, and while they separated in 1825, her death in 1830s affected him considerably.
Indeed, Lamb's hallmark was finding the middle ground. Though a Whig, he was offered the post of Irish Secretary by the Tory government in 1827. Upon the death of his father in 1828 and his becoming Viscount Melbourne, he moved to the House of Lords, but when the Whigs came to power under Earl Grey in 1830 he became Home Secretary in the new government.
Again, compromise was the key to Melbourne's actions. He was opposed to the radical governmental reforms proposed by the Whigs, and worked from within the party to prevent passage of the Reform Act. When Earl Grey resigned in 1834, Melbourne was widely perceived as the most widely acceptable replacement within the Whigs, and he soon became Prime Minister.
King William IV was opposed to the Whigs' reforming ways, however, and dismissed Melbourne in November. He then gave the Tories under Robert Peel an opportunity to form a government. As Peel had a minority in the House of Commons, however, it was essentially impossible for him to govern, and the Whigs (and Melbourne) returned to power in April, 1835.
The next year, Melbourne was once again involved in a sexual scandal. A friend of Caroline Norton, Melbourne was the victim of attempted blackmail from her husband -- George Norton. Norton demanded £1400, and when turned down accused Melbourne of having an affair with his wife. In Victorian times even one sexual scandal (like the one three decades earlier involving Byron) would be enough to finish off the career of most men, so it is a measure of the respect contemporaries had for his integrity that Melbourne's government did not fall. After Norton was unable to produce any evidence of an affair, the scandal died away.
Melbourne was therefore Prime Minister when Queen Victoria came to the throne. Barely eighteen, she was only just breaking free from the somewhat malevolent influence of her mother, the Duchess of Kent, and her mother's advisor, Sir John Conroy. Victoria was in desperate need of an advisor, and Melbourne supplied the answer. Over the next four years he trained her in the art of politics; any number of Victoria's actions were fraught with symbolic perils, and Melbourne spent most of his time with her helping her maneuver through the mine field. Every indication is that the two became friends -- Victoria was quoted as saying she considered him like a father (her own had died when she was only eight months old). Melbourne was given a private apartment at Windsor Castle, and rumours began to circulate that Victoria would marry Melbourne, forty years her senior.
In 1839 the Bedchamber Crisis occurred when Melbourne tried to resign and Victoria refused to dismiss the wives and daughters of Whig MPs who had made up her personal entourage. This led Robert Peel to refuse to form a new government, and Melbourne was persuaded to stay on as Prime Minister. Even after Melbourne resigned permanently in 1841, Victoria continued writing to him. This too was forbidden, however, as it was expected that the Queen should not show favour towards the party out of power. Eventually the correspondence was forced to an end, and Melbourne's role faded away as Victoria came to rely on her new husband Prince Albert of Saxe-Coburg as well as on herself.
Lord Melbourne passed away in 1848. Behind him he left a considerable list of reforming legislation -- not as considerable as that of Earl Grey, but worthy in any case. Among the acts passed during his administration were a reduction in the number of capital offenses, reform of the Poor Laws, and reforms of local government.