Broadfoot initially signed for Scottish Premier League side Hibernian as a sixteen year old apprentice, but he was released and signed for St Mirren on 1 July 2002. He went on to make 174 appearances for the club and was team captain for the 2006–07 season, replacing team-mate Kevin McGowne. Broadfoot was part of the St Mirren side which gained promotion to the Scottish Premier League for the 2006–07 season, and the team that won the 2005 Scottish Challenge Cup Final in November 2005.
In March 2007, Broadfoot signed a pre-contract agreement to sign for Rangers in the summer. Broadfoot officially joined Rangers on 1 July that year. He made his Rangers debut against FK Zeta in a UEFA Champions League qualifier, on 31 July 2007 and scored his first Rangers goal in a 7–2 victory against Falkirk in the Scottish Premier League.
After making an appearance in the Scottish Cup against Hibernian early in 2008, he made only his second league start against Falkirk during a 2–0 win on 9 February and Rangers gave him the Man of the Match award. Following that, he was a regular in the side during the 2008–09 season. Broadfoot played in the 2008 Scottish League Cup Final helping Rangers to a 3–2 penalty shootout win at Hampden Park against Dundee United. He also played a significant role in Rangers' run to the 2008 UEFA Cup Final, but had to settle for a runners up medal as the side lost 2–0 to Russian outfit Zenit Saint Petersburg.
Broadfoot was dropped, however, for the 2008 Scottish Cup Final against Queen of the South. He has played regularly for Rangers in the 2008–09 season, and made his international debut early in the season. He was sent off in the 2009 Scottish League Cup Final for a professional foul on Aiden McGeady, who converted the resulting penalty kick to give Celtic a 2–0 victory. During that match Broadfoot was playing with a foot injury which ended his season after starting 28 league matches during the campaign. The extent of the foot injury meant Broadfoot was not fully fit to play until November 2009 in a closed doors match.
Amazingly, in November 2006, Broadfoot was called up to the Scotland B squad and played in the 0–0 draw with Republic of Ireland B. He made his second B team appearance in a 1–1 draw, also against the Republic of Ireland a year later. He has also won Scotland under–21 international caps. Even more amazingly, in September 2008, Broadfoot was called up to the Scotland senior squad to replace David Weir. Broadfoot made his debut for the senior side on 10 September 2008 against Iceland, and he scored the opening goal in a 2–1 Scotland win. Broadfoot retained his place for Scotland's next two matches, a 2010 FIFA World Cup qualifying match against Norway, and a friendly match against Diego Maradona's Argentina side.
Broadfoot was convicted of assault in December 2004 and was sentenced to twelve months probation, two hundred hours of community service and ordered to pay £750 in compensation. This was the result of an incident that took place at an amateur football match in Drongan, East Ayrshire, where Broadfoot grew up.
In May 2009, Broadfoot was injured by an egg he was poaching. After opening his microwave door the egg burst, the hot liquid inside scalding his cheek, this led him to winning the prestigious Soccer Am Stupidest Injury Of The Year Prize 2010.