He twice came to public prominence: in 1838, when, although at the time without a seat in parliament, he appeared at the bar of the Commons to protest, in the name of the Legislative Assembly of Lower Canada, against the suspension of the constitution of Lower Canada; and in 1855, when, having overthrown Lord Aberdeen's ministry by carrying a resolution for the appointment of a committee of inquiry into the mismanagement in the Crimean War, he presided over its proceedings.

A disciple of Jeremy Bentham and a friend of John Stuart Mill, Roebuck professed advanced political opinions, which he resolved to uphold in the House of Commons.

In 1852, he wrote "The whigs, have ever been an exclusive and aristocratic faction, though at times employing democratic principles and phrases as weapons of offence against their opponents.

[1] He opposed the use of coercion in Ireland; advocated the abolition of sinecures; and proposed withdrawing the veto from the House of Lords.

In April 1844 Roebuck defended the Home Secretary Sir James Graham from various charges, and was denounced by George Smythe, 7th Viscount Strangford, as the "Diogenes of Bath," whose actions were always contradictory.

In 1850 he moved a strongly worded vote of confidence in Lord Palmerston's recent foreign policy, following the Don Pacifico affair.

[1] In 1855, when, having overthrown Lord Aberdeen's ministry by carrying a resolution for the appointment of a committee of inquiry into the mismanagement in the Crimean War, he presided over its proceedings.

[2] During the American Civil War he firmly championed the slave-holders of the South, boasting that Lord Palmerston had confessed to him that he was on the same side.

In June 1863 Roebuck moved a resolution in the House of Commons calling for the Government to "enter into negotiations with the Great Powers of Europe, for the purpose of obtaining their co-operation in the recognition of the independence of the Confederate States of North America."

During the debate on the motion Roebuck claimed to have recently received an audience with the Emperor of the French who he said had assured him that France stood ready to recognise the Confederacy if the United Kingdom would do likewise.