Lady Penelope O'Brien must have lived an interesting life, but I don't find a biography about her. The Oxford Directory of National Biographies about her dissolute husband is available; we can only imagine how much of it she experienced ... E.G., was she in Tangier?
Henry Mordaunt succeeded as the 2nd Earl of Peterborough two months after abandoning the captaincy of his father's horse troop in parliament's army for a command under King Charles.
Educated at Eton College (1635–8) and in France, his defection earned him command of a regiment of horse. He was seriously wounded at Newbury in 1643, but retained his command, serving at Cropredy and Lostwithiel (1644).
Also in 1644 he found time to marry Lady Penelope O'Brien.
He submitted to parliament after Naseby in 1645, and compounded for his estate, but a 1647 joined the Earl of Holland's ill-fated uprising in July 1648.
Peterborough escaped, but later compounded a second time.
During the 1650s he lived quietly in the country, trying to pay his debts.
After the Restoration he was rewarded with the governorship of Tangier. Appointed in 1661, he took possession in January 1662. He was recalled in December 1662 and was compensated with a £1,000 pension — which was rarely paid.
As early as 1663 Peterborough announced, ‘old notions of mixed governments’ were obsolete, and he advocated an expansion of the crown's authority (P. Seaward, The Cavalier Parliament and the Reconstruction of the Old Regime, 1989, 23).
As we know, in 1668 Lady Penelope complained ‘how they are forced to live beyond their estate and do get nothing by his [Peterborough's] being a courtier’, but Peterborough's friendship with James, duke of York paid off.
Peterborough volunteered aboard the Unicorn in the Second Anglo-Dutch War.
His connection with James became closer in 1673 when Charles II appointed Peterborough as ambassador-extraordinary to arrange his marriage to Mary of Modena.
Peterborough stood as James' proxy in the 1673 wedding, and escorted the new duchess back to England.
Peterborough's association with James resulted in accusations he played a role in the Popish Plot.
In 1678 he commanded a troop in York's regiment of horse.
He was dropped from the council in 1679, and he and Lady Penelope exiled in Brussels.
They were back in England by 1680, and he was against excluding James from the succession in the House of Lords.
He helped uncover the Rye House plot in 1683.
Peterborough carried the sceptre at James II's coronation and was awarded the Garter in June 1685.
Peterborough's military experience was important to James II, but it was his service as a courtier and political ally that made their relationship.
He was made groom of the stole and first gentleman of the bedchamber and in 1686 he became Queen Mary's high steward and chief bailiff.
Lady Penelope O'Brien Mordaunt, Countess of Peterborough was groom of the stole to Queen Mary of Modena
In March 1687 he converted to Catholicism. He was a witness at the birth of James, Prince of Wales in June 1688, and at the Glorious Revolution he fell with his mentor.
The Peterborough home, Dayton in Northamptonshire, was sacked by a mob, and in December he was captured at Ramsgate attempting to flee.
Imprisoned in the Tower from December 1688 to October 1690, Peterborough was impeached by the Commons in October 1689 (proceedings dropped).
He rejoined the Church of England in 1692 but remained a Jacobite; in April he asked permission to visit the exiled James II.
Past 70, he was under house arrest from February to March 1696 suspected of involvement in the assassination plot against William III.
An illness nearly killed him in September 1696, and thereafter his health declined. He died on 19 June 1697 and was buried at Turvey, Bedfordshire.
With his wife, Lady Penelope O'Brien (b. c.1622 - 1702), daughter of the 5th earl of Thomond, he had two daughters:
Elizabeth, never married,
and Mary (later Mary Howard), became duchess of Norfolk.
Peterborough ‘used his wife ill, … taking his pleasures elsewhere’, but in his later years, after his many reverses, he was described as behaving himself ‘humbly and sadly’ (Fitzherbert MSS, 268; Rutland MSS, 2.127)
The biography of Anne Lee Wharton (1659 - 1685), refers to "the unreliable autobiography of Goodwin Wharton (her brother-in-law) which said she had been "debauched when very young by Henry Mordaunt, 2nd earl of Peterborough."
Chart showing the number of references in each month of the diary’s entries.