During his youth, Smalling played for the Millwall academy before joining non-League club Maidstone United. After establishing himself in the Maidstone United first team, he signed for Middlesbrough in May 2008. However, shortly after joining Middlesbrough, Smalling had his contract with the club cancelled after raising concerns over homesickness. Soon after, in June 2008, he signed for Premier League club Fulham. He made his professional debut with them in May 2009 and helped them reach the 2010 UEFA Europa League Final the following season.