Royal marriages of the 19th century were arranged to secure alliances and to maintain blood ties among the European nations. As early as 1851, Queen Victoria of Great Britain and her consort Prince Albert were making plans to marry their eldest daughter, Victoria, Princess Royal, to Frederick. The royal dynasty in Britain was predominantly German; there was little British blood in Queen Victoria, and none in her husband. The monarchs desired to maintain their family's blood ties to Germany, and Prince Albert further hoped that the marriage would lead to the liberalization and modernization of Prussia. King Leopold I of Belgium, uncle of the British monarch and consort, also favoured this pairing; he had long treasured Baron Stockmar's idea of a marriage alliance between Britain and Prussia. Frederick's father, Prince William, had no interest in the arrangement, hoping instead for a Russian Grand Duchess as his daughter-in-law. However, Princess Augusta was greatly in favour of a match for her son that would bring closer connections with Britain.
The betrothal of the young couple was announced in April 1856, and their marriage took place on 25 January 1858 in the Chapel of St. James's Palace, London. To mark the occasion, Frederick was promoted to Major-General in the Prussian army. The newlyweds were compatible from the start and their marriage was a loving one; Victoria too had received a liberal education and shared her husband's views. The couple had eight children: William in 1859, Charlotte in 1860, Henry in 1862, Sigismund in 1864, Victoria in 1866, Waldemar in 1868, Sophie in 1870 and Margaret in 1872. Sigismund died at the age of 2 and Waldemar at age 11,[24] and their eldest son, William, suffered from a withered arm—probably due to his difficult and dangerous breech birth, although it could have also resulted from a mild case of cerebral palsy. William, who became emperor after Frederick's death, shared none of his parent's liberal ideas; his mother viewed him as a "complete Prussian". This difference in ideology created a rift between William and his parents, and relations between them were strained throughout their lives.