"Simmo" was drafted in the fourth round of the 2002 AFL Draft. He was Carlton's first pick in that year's draft, after the club was stripped of its higher selections as punishment for salary cap infringements. Carlton were so fortunate to have picked Simpson in the first place anyway, given his skills were immediately apparent, but he did not have enough weight to play regular seniors in his first two seasons; even now, his weight is a relatively light 79 kg. He played primarily for Carlton's VFL-affiliate, the Northern Bullants, in his first two years, and on his few selections in the Carlton senior team, received so little ground time that he did not have a disposal in his first three games.
Simpson first broke into the senior team as a regular in the latter half of 2005. Still eligible for the AFL Rising Star in his third season on the list, Simpson was nominated in Round 18. He played nine of the last 10 games of the season, missing one game through injury, and his pace and skill began to attract attention.
Simpson took a big step up in the 2006 season, being elevated to the leadership group and running 4th in the best and fairest. He played every game, mainly as a running link-man from half-back. He finished in the top 5 in the AFL for running bounces, which was typical of his rebound play, averaged 19 disposals with a maximum of 30, and eleven goals. This style of running play prompted Kevin Sheedy to select Simpson for the Australian International Rules team for the 2006 tour of Ireland, and Mick Malthouse to do likewise for in 2008, a series in which he won the Jim Stynes Medal.
By 2007, Simpson had emerged as one of the leaders of the club. He captained the Blues between Rounds 14 and 19 during 2007, in the absence of regular captain and vice-captain Lance Whitnall and Nick Stevens, and has been vice-captain to Chris Judd since Stevens' retirement.
In 2010, Kade Simpson had arguably his best season for the Carlton Football Club, polling nine Brownlow votes (Second for Carlton, behind medal-winner Chris Judd). The most noticeable feature of his performances during the season was his tackling ability, because on 12 occasions he laid five or more tackles.
Simpson played 158 consecutive games from Round 15, 2005, until Round 15, 2012, before missing a match with a broken jaw. He was, at the time, considered the club record holder for most consecutive games, but in December 2012, the AFL amended the interpretation of this record such that Bruce Doull, who missed two club games during his streak due to playing in interstate matches on the same day, assumed the club record with 162 consecutive games.
In the 2013 season, Simpson won the John Nicholls medal, Carltons best and fairest award. Kade had 533 disposals that season, after an outstanding year playing at half-back flank position under new coach Mick Malthouse.