In 1861, he was involved in the surveying operations prior to the construction of the Thames Embankment.[4] Two years later he was appointed under the 1863 Public Works (Manufacturing Districts) Act as an Assistant Commissioner (and later Inspector) of Public Works in Lancashire, during the Cotton Famine, and subsequently wrote A History of the Cotton Famine.[3][4][5] In his spare time he was a writer, and published two "sensation" novels: Ralph, or St Sepulchre's and St Stephen's (1863) and Hever Court (1867).[5]
He made a tour of southern and eastern Europe in 1867, and became a strong supporter of the Kingdom of Greece a position he set out in From the Levant. In 1873 he was awarded the Golden Cross of the Order of the Saviour of Greece.[4]
In 1867, he married Amelia Elizabeth Hyde of Castle Hyde, County Cork. They had no children. His wife was a campaigner for women's suffrage and a prominent public figure in her own right.[4]
He was a member of the Radical faction of the Liberal Party, and in 1868 was the first editor of The Echo, a Liberal evening paper. In 1873 was an unsuccessful candidate for a by-election at Huntingdon.[3] In 1875, soon after the sale of the Echo to Albert Grant, Arnold resigned his editorship and journeyed through the Middle East with his wife. He published an account of the thousand-mile journey in 1877 as Through Persia by Caravan.[3][4]