Hargan is well renowned for his away goal against IFK Göteborg in the UEFA Cup in 2006, which sparked a magical European campaign for the Candystripes culminating in a tie against french giants, Paris Saint Germain.

Hargan has scored more than 50 competitive goals for the Candystripes, including a decisive header away to IFK Gothenburg in the 2006 UEFA Cup qualifying round.

Hargan was described as a great servant for the club and is mostly remembered for the goal he scored in the UEFA Cup tie (now Europa League) against Swedish giants IFK Gothenburg, which saw Derry City to a 1–0 victory on the night.

After Derry's City's European experience which included memorable ties with Gretna and PSG, Shelbourne were reported to have shown interest in the left back, but Hargan pledged his loyalty and stayed with the Candystripes until the end of the 2008 season.

Dungannon Swifts and Coleraine were also believed to be interested in the veteran full-back, but Hargan signed for the Crues and spent just under a year as his career was cut short due to injury.