[2] In 1819, on his return to political life, he pressed for establishing a more efficient bankruptcy court, and of expediting the recovery of small debts; and he saw both these reforms accomplished before 1825.

During the greater part of the reign of George IV, the Whigs lost their influence in the state from their want of cohesion, but this defect was soon remedied in 1830 when Lord Althorp was chosen their leader in the lower house, and his capacity for the position was proved by experience.

Along with Lord John Russell, he led the fight to pass the Reform Bill of 1832, making more than twenty speeches, and is generally considered the architect of its victory.

He was a notable cattle breeder and the first president of the Royal Agricultural Society which was founded in 1838, the year he paid homage to Queen Victoria at her Coronation.

On 13 April 1814, Spencer married Esther Acklom (September 1788 – 11 June 1818) at Upper Brook Street, Mayfair, London.

Cokayne quotes from the Farington Diaries, "in marrying He complied with the wishes of Lord and Lady Spencer, it was not of His own seeking" and from the Letter Bag of Lady Elizabeth Spencer-Stanhope, "since Jack Althorp would not propose to her, she proposed to him; and such an unusual proceeding was fraught with happy consequences ... his devotion after marriage amply compensated for his lack of ardour before."

John was said to be deeply upset by his wife's death and was devoted to her memory for the rest of his life: he resolved never to remarry, and it is said that he gave up hunting, his favourite pastime, to mark the depth of his loss.