Michael MacCartney, from Letchworth in the UK, was taken into custody in Alicante.
Police arrested the man after receiving a call from a resident of the city saying they had seen MacCartney's face on a television news programme, Spain's La Razón newspaper reported.
The 78-year-old MacCartney was found guilty of indecent assault, indecency with a child and inciting sexual activity involving penetration in March but failed to show up in court for sentencing.
MacCartney is one of the 'Unlucky 13' — a group of men wanted by UK authorities believed to be hiding in Spain.
The list also contains figures wanted for crimes including drug trafficking and robbery.
The group are part part of the long-running Operation Captura, designed to bring justice to UK fugitives in Spain.
People with information calling from Spain can use a special freephone Spanish 900 555 111 telephone number which will be answered in the UK by Crimestoppers’ call agents and a translation service is available upon request.
People can also pass on information anonymously via the Crimestoppers number 0800 555 111 or online at www.crimestoppers-uk.org.