Jardine played in various defensive positions as he became a regular under manager Davie White, even as a centre-forward, before finally settling as a right full-back at the start of the 1970–71 season. His first major trophy was at this position in the 1970 Scottish League Cup Final. The position was where he made the bulk of his 674 appearances for the club. He also was right full-back in the famous team which won the 1972 European Cup Winners' Cup Final, playing in all eight matches en route to the final and scoring the first goal of a 2–0 win over FC Bayern Munich in the semi-final.
In 1982, in the twilight of his career, he joined his boyhood team Hearts, linking up with former Rangers team-mate Alex MacDonald who was now player-manager at the Edinburgh club. Jardine went on to make over 200 appearances for the Jambos and was an integral part of the side that came so close to winning the league championship in 1986. Indeed, Jardine's performances that season saw him at the age of 37 win the Scottish Footballer of the Year award.
Jardine later worked for Rangers in a public relations capacity and then in the retail department as the club's sales and marketing manager. On 26 April 2012 Jardine was reported by the BBC as having met with Rangers supporters groups to plan "taking sanctions" against other Scottish Clubs. The BBC reported that he said, "... the supporters will take sanctions against clubs which we deem to have been unfair to ourselves."