Sean Fallon, who has died aged 90, was assistant to the Celtic manager Jock Stein throughout a glorious era when the Glasgow club became the first in Britain to win the European Cup and achieved a record-breaking nine successive Scottish League titles. Fallon's association with Celtic spanned seven decades, from signing as a player in 1950 to receiving an emotional reception when unfurling the League flag over Celtic Park at the start of the current season. All that time in Scotland never diluted the rich accent of his native Sligo.

Of the team who defeated Inter Milan in Lisbon in 1967 to win the European Cup, 10 had been signed before Stein's return to Celtic as manager two years earlier. While Stein's genius lay in turning a squad of players, all from within 40 miles of Glasgow, into a world-beating side, the role of Fallon in assembling it was crucial.

Like many young Irishmen, Fallon was forced into a choice between Gaelic football, in which he excelled, and the association code. As a rugged defender, he signed for Sligo Rovers in the League of Ireland and then Glenavon in Northern Ireland, quickly attracting attention from across the water.

Fallon had been educated in Sligo by Catholic Marist Brothers and was familiar with the role of Brother Walfrid, a Marist from Ballymote, County Sligo, in the foundation of Celtic for charitable purposes in the East End of Glasgow. There was, he said, no other club he wanted to play for.

This was just as well, since Celtic's signing-on terms were less than generous. The manager, Jimmy McGrory, offered Fallon £10 a week, falling to £8 in the close season. At that time, he was earning £6 with Glenavon and £8 in his trade as a confectioner, but the lure of Celtic was strong enough to seal the move.

While McGrory was nominal manager and a revered former player, it was Celtic's chairman, Bob Kelly, who called the shots in all aspects of the club's affairs. Kelly was a devout Catholic and marked 1950, Holy Year, with a European tour which culminated in an audience with Pope Pius XII.

Fallon recalled that this involved a cross-Channel ferry on which Bing Crosby was a fellow passenger. By the time they reached port, Crosby was singing I Belong to Glasgow at the bar. After a three-day train journey, a solitary game with Lazio was followed by the appointment at St Peter's – the true purpose of the expedition.

This curious close-season tour was indicative of the way Celtic operated and was reflected in an increasingly bleak record of success. However, seeds of future glory were sown with the recruitment of Stein from the obscurity of Welsh non-league football. When Fallon suffered injury in 1953, Stein – whom he had nominated – succeeded him as team captain.

Fallon made 254 Celtic appearances and was known as "the Iron Man" in tribute to his uncompromising style. He won just one League and two Scottish Cup medals, as well as eight Irish caps. The highlight of his playing career was as a member of the team that beat Rangers 7-1 in the League Cup final of 1957-58.

Fallon joined the backroom staff and, along with Stein, developed a youth policy that was to prove highly fruitful, yielding such eventual Lisbon Lions as Billy McNeill, John Clark and Bertie Auld. With Stein's departure in 1960 to manage Dunfermline and then Hibs, Fallon became assistant to McGrory and established his reputation as a spotter of exceptional talent.

He was mooted as McGrory's successor but showed no resentment when Stein was brought back. The two retained a close personal bond and acted as perfect foils – Fallon the quietly spoken conciliator while the harder-edged Stein dealt brusquely with those who merited his ire. Fallon was instrumental in signing another generation of Celtic stars including David Hay, Kenny Dalglish and Paul McStay.

When Stein suffered a serious car accident in 1975, Fallon became temporary manager, but the longer-term appointment fell to Billy McNeill and Fallon departed. He had a brief managerial spell with Dumbarton but maintained ties with Celtic, where he was treasured as a gentleman of the game.

In 2002, Fallon received the freedom of Sligo. He is survived by his wife, Myra, five daughters and a son.

• Sean Fallon, footballer and coach, born 31 July 1922; died 18 January 2013