Slade made his debut for Canterbury playing first five in the 2008 Air New Zealand Cup, and scored 86 points for his side as Canterbury won the competition. His performances improved substantially as the season progressed and with Dan Carter unavailable and Stephen Brett injured, Slade became the first choice 10 for the Canterbury side.

Slade’s performance in the 2008 Air New Zealand Cup caught the eye of Crusaders coach Todd Blackadder who included Slade into the squad for the 2009 season. Playing mainly out of position on the wing, he emerged as a regular member of the squad, making 11 starts as well as a substitute appearance in the semi-final against the Bulls.

In the 2009 Air New Zealand Cup, Slade was shifted to fullback as Stephen Brett was again healthy and reclaimed the number 10 jersey. Despite the shift in position, however, Slade didn’t miss a beat as he started 14 games as one of the leading fullbacks in the competition, scoring 4 tries over the course of the season (including two outstanding tries in the final) as Canterbury again emerged champions.

For the 2010 ITM Cup, Slade reclaimed the starting first five position for Canterbury – along with first-choice goal-kicking duties – and emerged as one of the most dominant players in the competition. Despite missing games while with the All Blacks, Slade scored 152 points in just 11 starts to finish 2nd in the competition to Lachie Munro. He also led Canterbury to their third consecutive title, sealing victory in the final against Waikato with a fine individual try.

For the 2010 Super 14 season, Slade was shifted to fullback, as he had been in the previous Air New Zealand Cup. His season was highlighted by a 21-point performance against the Lions on 20 March and his first Super Rugby try against the Stormers on 20 April.

In 2010, Slade was called up again as a replacement for injured fly-half Dan Carter for the All Blacks final match in the 2010 Tri-Nations against the Wallabies on 11 September. He made his All Black debut off the bench in the 60th minute coming on as a replacement for Aaron Cruden.

Slade then made a mark in New Zealand’s friendly against Fiji in July 2011. He scored a try, two penalties and four conversions for the All Blacks. He then played in New Zealand’s opening Tri-Nations game against South Africa and scored New Zealand’s sixth try of the match, resulting in victory by 40–7. He came on as a substitute in New Zealand’s next match against Australia. He got his first Tri-Nations start against South Africa in the All Blacks penultimate game.

During the 2014 game against the Springboks at Ellis Park Slade played in the unfamiliar position of halfback due to injury to the replacement halfback Tawera Kerr-Barlow. He also kicked a last minute conversion in the All Blacks final Bledisloe Cup match against Australia in Brisbane. Slade was also called into the End of Year Tour and started a test match on the right wing and also made a strong appearance from bench in the All Blacks final game against Wales in Cardiff.

The 2015 super rugby season was another strong season for Slade managing again establish himself as the number 10 for the Crusaders. However, the Crusaders season would not go to plan, failing to make the playoffs.

In 2015 Slade was named in the 2015 World Cup All Black squad only playing against Namibia on the road to winning the title.

On 14 April 2015, it was announced Slade had signed a two-year deal with French Pro D2 side Pau as the team was promoted to Top 14.