Sykes joined HM Foreign Service in 1947 and served at the Foreign Office from 1947 to 1948. He then served in Nanking, Peking and returned to the UK to serve at the Foreign Office. His next overseas postings took him to Brussels, Santiago and Athens, before returning to the Foreign Office. Sykes' first posting as an ambassador came with a posting to Havana before moving to be a Minister at the British Embassy in Washington D.C.. From there he returned to the Foreign Office as Department Under-Secretary between 1975 and 1977. Sykes was then appointed as Ambassador to the Netherlands in 1977.
Assassination
Sykes was leaving his residence in The Hague at 9 am and was getting into his silver Rolls Roycelimousine when he was shot. He was sitting next to Alyson Bailes. The car door was held by Karel Straub, a 19 year old Dutch national who worked at the embassy. Staub was also shot in the attack. Sykes' chauffeur, Jack Wilson, was uninjured and drove Sykes to Westeinde Hospital where he died two hours later. Straub was transported by ambulance to the same hospital where he also died. Police reported that the shots came from around 10 yards by two assailants wearing business suits who escaped on foot following the attack. Suspects for the assassination were Palestinians or Iraqis, although no evidence was ever put forward. It was ultimately confirmed that the IRA had carried out the killings. The IRA claimed responsibility for the assassination in February 1980. In a statement they said of Sykes: " not just a Brit propagandist, as are all British ambassadors, but because he had been engaged in intelligence operations against our organisation." The 'intelligence operations' mentioned in the statement related to a government report written by Sykes following the assassination of Christopher Ewart-Biggs. Ewart-Biggs was the British Ambassador to the Republic of Ireland and was killed by the IRA in 1976. Sykes produced diplomatic security guidelines as part of his report. Sykes' position as Ambassador to the Netherlands had been strained due to certain Dutch groups, which were sympathetic to the IRA, and consequent arms smuggling activities.
Family
Sykes was married to Ann, Lady Sykes. The couple had three children. Lady Sykes died in 2018.