It deals with British politics of the 1860s, including voting reform, secret ballot, rotten boroughs, and Irish tenant-right, as well as Finn's romances with women of fortune, which would secure his financial future.

Volume I: In Killaloe, County Clare, Phineas Finn is the only son of a successful doctor who can afford to send him to London to study law.

Within the social circle of his fellow MPs, he falls in love with Lady Laura Standish, the wealthy daughter of a prominent Whig politician.

Lady Laura convinces her father to let Finn stand for the family borough of Loughton, since her brother is uninterested in representing it.

In October 1867, the very month that Phineas Finn began its serial run, Trollope resigned his position in the General Post Office.

[1]: xvi  Ironically, the Beverley election was set aside and the seat voided because of bribery, touching on some of the central issues of Trollope's novel.

In order to enable him to shift the focus of the cycle more towards Parliament, Trollope was given permission by the Speaker of the House of Commons to observe proceedings for several months.

[3]: 274 Trollope covers a wide range of current political issues in Phineas Finn, such as the construction of the Canadian Pacific Railway, the War Office's procurement process, disestablishment of the Irish Church, and corrupt electoral practices such as treating.

The novel sends up the vacuity of politics by showing Liberals and Conservatives voting against their own stated positions when they see a tactical advantage in doing so.

The bill was designed by Liberal Prime Minister Earl Russell to increase the voting population by 40% and resolve issues such as rotten boroughs, which had not been fully addressed by the Reform Act 1832.

Disraeli's Act ended up doubling the voting population and led to the Liberal Party returning to power in the election of 1868.

Initial reviews immediately speculated on the real identities of Trollope's characters, and scholars have continued the guessing game.

[10][9]: 132–3  One common suggestion for the inspiration for the character is John Pope Hennessy, a Roman Catholic from Cork, who was elected as an Irish Nationalist Conservative MP for King's County in 1859.

[11] Since the publication of the book, conjectures have pointed to a wide range of people including John Sadleir, Chichester Fortescue, William Gregory, Colonel King-Harman, and Isaac Butt.

[13] Partially because Madame Max Goesler and Phineas marry in Redux, her character is often surmised as a gloss on Frances, Dowager Countess Waldegrave, who made Chichester Fortescue her fourth husband.

However, it did praise Lord Chiltern as a near peer of the "indelible" George Vavasor in Can You Forgive Her?, and felt that Mr. Kennedy "is as wonderful a picture as Mr. Trollope has yet drawn.

"[18] The Saturday Review panned the novel primarily because of its portrayal of Mr. Turnbull, whom it deemed to be a thinly disguised version of John Bright.

Bright that acts upon Mr. Trollope as a red rag upon a bull," and they excoriate the practice of violating the confidence of a politician's "after-dinner conversations and habits".

The review concludes that Phineas Finn's only utility will be so a "future historian may refer to it to discover what was the material of which Mr. Bright’s waistcoats were made.

Comparing his practice, and that of Benjamin Disraeli, to witches tormenting wax figures, the Telegraph said, "The author of Vivian Grey did something utterly indefensible when he introduced public men as characters in his tales.

"[21] The Dublin Review had high praise for the novel and Trollope's writing in general, "He holds a place, not only unrivalled, but undisputed, as the realistic portrayer of the middle classes of English society."

Their review praised his knowledge of "the machinery of Parliament" and the issues of "the land question in Ireland", which they felt exceeded the familiarity of average Irishmen themselves.

They found the novel such a sympathetic portrait of Ireland that they urged, "some Irish constituency should do itself the honour of gratifying Mr. Trollope's unaccountable desire to enter Parliament.