Holborne had spent some time as a Marshal and a Reader at Lincoln's Inn, which he first entered in 1615, after his training at Furnival's Inn. He was not called to the bar until 1624, after a not unusual period of preparation. In 1622 the young lawyer had become Steward for the Sussex Manor of Bosham which it appears he inherited from his father, Nicholas of Chichester.
Holborne was married (1630-3) to the Lady Anne Dudley, grand daughter of the famous Earl of Leicester. Lady Anne was one of the abandoned daughters and co-heirs of Sir Robert Dudley, formally of Kenilworth Castle, Warwickshire, Ist Duca de Northumbria. It has been suggested this relationship may have influenced his initial anti-Court reputation.
He was proposed by the Viscount (Thomas) Savile and elected to the Short Parliament, for Southwark "on the basis of his reputation as foe of the King and of oppression," his popular reputation having been assured by his bold and protracted defence of Hampden. As one of the MP's in favour of the fullest consideration of grievances, he played a prominent part in the Short Parliament being named to eight Committees including Privileges.
Savile supported Holborne putting it about that the Lawyer "did always oppose the King, the Ship Money, and all monopolies whatever." He was dispatched along with Oliver Saint-John to require the King's Judges to give up records concerning the Ship Money case relating to Hampden.
What was later to be called the Long Parliament was summoned in 1640, in a bid to secure funds for the King, and the elections, as such they were, came to be fought chiefly on the basis of the candidates stand, being either for Parliament or for the King. The result being a crushing defeat for the King, even in such Royal strongholds as Cornwall where Holborne was successfully returned as a Royalist.
In May 1641 an "Act against the dissolution of this Parliament without it’s own Consent" was passed, in July the King compelled by his guilt in signing away the life of Wentworth was forced to accept the abolition of the Prerogative Courts of Star Chamber and High Commission and in August Ship Money was finally declared illegal.
Holborne, was manager of the conference on two bills to abolish The Star Chamber, which like the other conciliar courts which had been introduced into England under the Tudors adopted the Inquisitorial procedure which was unknown in the English Common Law Courts.
For his part, Holborne had clearly dispelled any rumours that he might oppose the right of the Court by defecting to the King not that long after these events. From 1640-42 serving as a JP for Middlesex, Holborne's radical thinking had been softened by a change in loyalties.
Holborne sat as an MP in the Long Parliament for the Cornish borough of Mitchell, where the Arundels of Trerice had an interest after John Arundel II, himself also closely connected with Lincoln's Inn, had announced his intention of standing for the Seat of Bodmin was duly elected and returned to Westminster, thereafter no longer associated with the popular cause.
His change of loyalties to the crown may be seen as an act of personal ambition for it was after the dissolution of Parliament that it was already rumoured he might be chosen as the Solicitor General, but for his distinct differences with the Court.
He gained five committee appointments, and this time four of them were chiefly concerned with the Authority of Convocation and reform of the Church, which he opposed. He made a learned legalistic argument on behalf of the Bishops who only four years earlier he would have opposed.
He wished to defer Pym's motion to vote the ecclesiastical cannons as illegal and in their defence made a two hour speech in which he supported convocations right to bind both clergy and laity with the Consent of the Crown, stating: "Surely the Church ought to be governed by itself, and the layman not to intermeddle in it...such cannons as were directly against the law were void, but such as constitute indifferent things are not against the law but ought to bind."
The Presumptions of Parliament now replacing those of the Laudian Clergy, he took the Protestation. After the recess his support for the Church and the King's Rights was uncompromising and he was among those recommended to the King by Secretary Nicholas as one of the Chief champions of the Royal Prerogative, and opposed the Grand Remonstrance, considering Parliament to be over-stretching its own authority. He argued: "A Parliament may do a thing unlawful, as to change our Religion, and then we are bound to ask leave to protest against it".
Robert had previously distinguished himself on February 28, 1641 with The reading in Lincoln's Inne upon the statutes of treason. His Discourse on Treason was subsequently published by an Oxford printer as Royalist propaganda about the time he was expelled from the House along with other Royalists, although he had not been present therein for the best part of that summer of 1642.
In his younger days the rising Lawyer was said also to have been a great lover of Astrology, "having experienced the truth of it thereof himself." The practice had perhaps reached its peak during the Civil War and Interregnum with its most celebrated exponent being William Lilly. During these times astrology became an essential aspect of the intellectual framework in which men were educated, that Robert then was keen to see what fated his future with the Lady Anne Dudley may also have played some part in his later political judgements.
Given the illustrious ancestry of the Earl of Leycester, son of John Dudley the Lawyer Robert Holborne would have had no doubt as to the implications of his marital status, yet he and the Lady Anne do not appear to have had any children.
In his Horoscope "a long journey by sea or land" is said to have been predicted for him in the November of 1642, yet from whence he came to join the King at Oxford is uncertain. It was their he sat in the Oxford Parliament and at this point in his journey through life was made Attorney General to the Prince of Wales (Prince Rupert) and a member of his Council.
It has further been suggested that his late loyalty to the Crown may have been a consideration in the granting of a Patent to his Mother in Law, the Lady Alice Dudley, a woman of noted piety and charity, which conferred on her the Dignity of a Duchess and the Precedence of a Duke's daughter on her children.
In 1643 the MPs who were Royalist joined the King at Oxford. His professional ambition may have motivated Holborne to be amongst this group. The King, who would no doubt have known of Holborne's legal abilities personally created him a Knight at Oxford in 1643.
Sir Robert Holborne was disabled as a Royalist on January 22, 1644, soon to return however as a Commander for the King at Uxbridge in 1645. He was present Sturbridge at the peace negotiations as an advisor to the King. He filled the role of Attorney General to the Prince, from 1644 to 1646 as well as being an ordinary member of the Council of the Prince of Wales, who was then Prince Rupert.
Holborne is recorded as having died aged 50, having spent his last days at Covent Garden. It has been said that he was buried at night in Lincoln’s Inn Chapel on February 16, 1648, but he is mentioned on the monument of Lady Anne at St Giles.
The estates of those MPs, such as Holbourn, who later demonstrated their loyalty to the King were subsequently subject to sequestration by the reforming Parliamentary Committee. Their can be no doubt that by 1650 a great many Gentry had similar retributions placed upon them leading many into a "terrifying web of debt."