Probably born in Suffolk, Sexby fought in Oliver Cromwell's regiment of Ironsides during the First CIvil War and transferred to Lord-General Fairfax's regiment of horse on the formation of the New Model Army in 1645. By 1646, he was a follower of John Lilburne, visiting Lilburne during his imprisonment in the Tower of London and helping to get his pamphlets printed and circulated. Sexby played a leading role in spreading Leveller doctrines in the Army and in setting up the Council of Agitators to petition for soldiers' rights. He was one of the three Agitators who presented the soldiers' grievances to the House of Commons in April 1647 and was a member of the army delegation sent by Fairfax to lay charges against the Eleven Members in July. Sexby was a prominent speaker at the Putney Debates (October-November 1647), where he denounced the Monarchy and argued the case for democratic rights for the soldiers who had fought for Parliament.
After the Second Civil War, Sexby grew impatient with the Levellers' opposition to the King's trial and execution. He became an active supporter of the Commonwealth and was appointed governor of Portland Castle. In June 1650, he took command of a regiment raised for service in Ireland but subsequently sent to Scotland. Sexby's regiment served under General Monck at the siege of Tantallon Castle in the spring of 1651. However, his career as a Grandee came to an abrupt end in June 1651 when he was court-martialled and cashiered for a number of irregularities, including the witholding of pay from his troops.
In the autumn of 1651, Sexby was employed as the Commonwealth's agent in France where he tried to negotiate an alliance with the Frondeurs, but he found that the Fronde rebellion had deteriorated into factional fighting between French noblemen with no interest in proclaiming a republic. He encouraged the Frondeurs to adopt an adapted version of the Agreement of the People, but the authorities at Bordeaux ordered his arrest. Sexby narrowly escaped by climbing over the town wall at night.
Sexby violently opposed Cromwell's elevation to the office of Lord Protector in 1653 and began actively plotting against the Protectorate. Pursued by government agents, he travelled all over southern England distributing pamphlets denouncing Cromwell. He attempted to form alliances between all parties that were hostile to the Protectorate: Royalists, republicans of the old Commonwealth, disillusioned Levellers and Presbyterians. After almost being arrested in 1655, Sexby escaped abroad and tried to raise Spanish support for an insurrection to bring down the government of England. Although he was well-received at Madrid, the Spanish government was reluctant to commit troops and money to the enterprise. At Bruges, Sexby attended Charles II's court-in-exile, proposing to lead an uprising against Cromwell. Sir Edward Hyde was sceptical, realising that Sexby's proposal to unite Royalists and Levellers had little practical chance of success.
Sexby co-authored a pamphlet: Killing no Murder, which argued with biblical and classical examples that tyrannicide was justifiable and that Cromwell was a tyrant. He became involved in plots to assassinate Cromwell, employing Miles Sindercombe to carry them out. After the failure of several attempts to shoot Cromwell in 1656, Sindercombe and his accomplices were arrested when their scheme to set fire to Whitehall was betrayed. In June 1657, Sexby himself came to England, intending to instigate new conspiracies against Cromwell. Thwarted by the vigilance of Thurloe's agents he decided to return to Flanders, only to be arrested as his ship was about to sail. Sexby was imprisoned in the Tower of London. Under interrogation he admitted to being the author of Killing no Murder and to his involvement in the assassination plots, but he refused to name his accomplices. He died of a fever in January 1658 before being brought to trial.
References:
C.H. Firth, Edward Sexby, DNB, 1897
C.H. Firth, The Last Years of the Protectorate, 1656-58, vol. i, 1909
Alan Marshall, Edward Sexby, Oxford DNB, 2004