 Lappin was an unused substitute in several games during St Mirren's 2000–01 Scottish Premier League campaign.After relegation that season he was fast-tracked into the first team where his precision crosses from the left, both in open play and from set pieces led to a number of goals for teammates.He made the first of his ten Scotland Under-21 appearances during 2003–04 the season and helped the club gain promotion to the Scottish Premier League for 2006–07, after which he signed a two-year contract extension.