Herschell's school-day reputation persisted after he became a law student at Lincoln's Inn. In 1858 he entered the chambers of Thomas Chitty, the famous special pleader. His fellow pupils included Archibald Levin Smith, subsequently Master of the Rolls, and Arthur Charles who became a judge of the Queen's Bench. He subsequently read with James Hannen, who went on to become Lord Hannen. His fellow pupils gane him the sobriquet "Chief Baron" because of his air of superiority. In 1860 he was called to the bar and joined the northern circuit.
For four or five years he did not obtain much work. Howevere he was financially secure, and had no need to supplement his legal income with journalism or writing. Two of his contemporaries, each of whom achieved eminence themselves, found themselves in similar circumstances, One of these, Charles Russell, ultimately became Lord Chief Justice. The other, William Court Gully became Speaker of the British House of Commons. It is said that these three friends, dining together during a Liverpool assize some years after they had been called, agreed that their prospects were anything but cheerful. It is likely that about this time Herschell meditated quitting England for Shanghai and practising in the consular courts there. Herschell, however, soon made himself useful to Edward James, the then leader of the northern circuit, and to John Richard Quain, the leading stuffgownsman. For the latter he noted briefs and drafted legal opinions. When, in 1866, Quain took silk, Herschell inherited mush of his junion practice.
By 1874 Herschell's business had become so good that he turned his thoughts to politics and election to Parliament. In February of that year there was a general election, with the result that the Conservative Party came into power with a parliamentary majority of fifty. The usual crop of election petitions followed. The two Radicals, Thomas Charles Thompson and John Henderson who had been returned for City of Durham were unseated, and an attack was then made on the seats of two other Radicals, Isaac Lowthian Bell and Charles Mark Palmer who had been returned for North Durham. Herschell was briefed for one of the latter. He made such an impression on the local Radical leaders that they asked him to stand for City of Durham. After two week's electioneering, he was elected as junior member. Between 1874 and 1880 Herschell was assiduous in his attendance in the House of Commons. He was not a frequent speaker, but a few efforts gained for him a reputation as a debater. The best examples of his style as a private member are found in Hansard under the dates February 18, 1876, May 23, 1878, and May 6, 1879. On the last occasion he carried a resolution in favor of abolishing actions for breach of promise of marriage except when actual pecuniary loss had ensued, the damages in such cases to be measured by the amount of such loss. He was noticed by Prime Minister William Ewart Gladstone, who in 1880 appointed Herschell Solicitor General.
Lord Herschell's judgments were distinguished for their acute and subtle reasoning, for their grasp of legal principles, and, whenever the occasion arose, for their broad treatment of constitutional and social questions. He was not a profound lawyer, but his quickness was an excellent substitute for great learning. In construing a real property will or any other document, his first impulse was to read it by "the light of nature", and to decline to be influenced by the construction put by the judges on similar phrases occurring elsewhere. However, when he discovered that certain expressions had acquired a technical meaning which could not be disturbed without fluttering the dovecotes of the conveyancers, he would yield to the established rule, even though he did not agree with it.
He was perhaps seen at his judicial best in Vagliano v. Bank of England (1891) and Allen v. Flood (1898). Latterly he showed a tendency to interrupt counsel overmuch. The latter case is an example of this. The question involved was what constituted a "molestation of a man in the pursuit of his lawful calling". At the close of the argument of counsel, whom he had frequently interrupted, one of their lordships observed that although there might be a doubt as to what amounted to such molestation in point of law, the House could well understand, after that day's proceedings, what it was in actual practice.
In June 1893 he was appointed chancellor of the University of London succeeding the Earl of Derby. His views of reform, according to Victor Dickins, the accomplished registrar of the University, were liberal and frankly stated, though at first they were not altogether popular. He disarmed opposition by his intellectual power, rather than conciliated it by compromise, and sometimes was perhaps a little forceful in his approach various matters of controversy.
His characteristic power of detachment was well illustrated by his treatment of the proposal to remove the university to the site of the Imperial Institute at South Kensington. Although he was then chairman of the Institute, the most irreconcilable opponent of the removal never questioned his absolute impartiality. Herschell had been officially connected with the Imperial Institute from its inception. He was chairman of the provisional committee appointed by Edward Prince of Wales to formulate a scheme for its organization, and he took an active part in the preparation of its royal charter and constitution in conjunction with Lord Thring, Lord James, Sir Frederick Abel and John Hollams. He was the first chairman of its council, and, except during his tour in India in 1888, when he brought the Institute to the notice of the Indian authorities, he was hardly absent from a single meeting. For his special services in this connection he recevied the Order of the Bath in 1893, this being the only instance of a Lord Chancellor being decorated with an order. In 1893 he became, at its foundation, president of the Society of Comparative Legislation.
In 1897 he was appointed, jointly with Lord Justice Collins, to represent Great Britain on the Venezuela Boundary Commission, which met in Paris in the spring of 1899. Such a complicated business involved a careful study of maps and historic documents. Not content with this, he accepted in 1898 a seat on the joint high commission appointed to adjudicate in the Alaska boundary dispute and to adjust boundary and other important questions pending between Great Britain and Canada on the one hand and the United States on the other hand. He started for the U.S. in July of that year, and was received cordially at Washington D.C.. His fellow commissioners elected him their president.
A funeral service held in St John's Episcopal Church, Washington, was attended by the president and vice-president of the United States, by the cabinet ministers, the judges of the Supreme Court, the members of the joint high commission, and a large number of senators and other representative men. The body was brought to London in a British man-of-war, and a second funeral service was held in Westminster Abbey before it was conveyed to its final resting-place at Tincleton, Dorset, in the parish church of which he had been married.
Herschell left a widow, granddaughter of Vice-Chancellor Kindersley; a son, Richard Farrer Herschell (b. 1878), who succeeded him as second baron; and two daughters.