According to the Cambridge News website in January 2002, Cambridge City's 16 year old Robbie Simpson was signed from Norwich City's youth setup and made his full debut for Cambridge City in Jan 2002 aged 16.. Originally a midfielder, Robbie has been converted into a centre forward.

On 2nd June 2006, Robbie moved across the city of Cambridge to join Rob Newman's Cambridge United.

In April 2007, speculation suggested that Norwich are one of three Championship clubs running the rule over Cambridge United striker Robbie Simpson who has hit 13 goals in his last 14 matches for the Nationwide Conference outfit alerting the likes of Ipswich Town and Leicester City along with Canaries manager Peter Grant. Robbie is due to sign for Coventyr on 1st July 2007 with the fee to be decided by tribunal as Cambridge boss Jimmy Quinn claims the two clubs are "a million miles apart" in their valuation of the player. On 9th July, the FA set compensation for the move. Coventry will pay £40,000 initially, with an overall fee of £130,000 possible dependent on appearances and a 5 percent sell-on clause agreed for the 22-year-old striker. This was blasted by Cambridge chairman Lee Power "But the biggest kick in the teeth is the sell-on of just 5%. I've never known such a low sell-on in my life; they're normally much higher - 15% or 20%. They know the lifeblood of any smaller football club is the sell-on in a case like this, and they've given the player away on our behalf for £40,000 and then given us nothing to look forward to in the future with the sell-on. It's an absolute disgrace and I'm livid. I don't know yet if there is an appeal process but we'll find out,"

During 2008/9. Simpson was used mainly on the right wing by Chris Coleman, after slipping behind Leon McKenzie, Leon Best, Freddy Eastwood and Clinton Morrison in the pecking order for striking spots. His cause was not helped last season by a thigh strain, but he still made 37 appearances and scored five goals from the flank as Coventry's play-off push never quite materialised

In June 2009, Simpson was rumoured to be part of a deal that would take Norwich's Sammy Clingan to the Ricoh Stadium. Knebworth-born Simpson is regarded as a target man and at 6ft 1in would probably fit Gunn's requirements for a big front man, after Carl Cort, Chris Killen, Alan Lee, Antoine Sibierski and Darel Russell tried with varying degrees of success last season. Instead Robbie signed for Lee Clark's Huddersfield for a sum reported to be £300,000

Simpson was loaned to Brentford for the 2010-11 season on 6th August 2010, making 27 league appearances and scoring 4 goals.

Simpson joined Oldham Athletic on loan on 10th September 2011. He made 14 appearances, scoring three times, before his loan ended on December 12, but Huddersfield allowed him to stay at Oldham in a training capacity. He rejoined Oldham on loan, until the end of the season, on 1st January 2012. The loan was made permanent on 30th January 2012.

Simpson was one of five Oldham players released by the club on 1st May 2013. He scored 13 goals in 80 appearances. Manager Lee Johnson said it was a hard decision to make. "Robbie has been fantastic during the short time I have been here. I like him as a person and he gave everything whether in a match or on the training pitch. It is a measure of how highly I regard Robbie that I made him captain when James Wesolowski was ruled out. And as I have mentioned before, if you were in the trenches, Robbie is the sort of character you would like alongside you."

Simpson signed a two month deal with Leyton Orient on 11th November 2013. "Robbie could prove to be a really handy signing for us," said O's manager Russell Slade. "We know we have a small squad so need players that are versatile and he can play up front or in midfield. Plus he's a great character to join the group." He had previously trialled with Blackburn Rovers (October 2013) and Sheffield Wednesday (November 2013).

At the end of the 2013/14 season, after appearing on the bench for the 2014 Football League One play-off Final, he was released by Orient along with four other players.

On 9th June 2014, Simpson re-joined newly promoted League Two side Cambridge United on a two-year deal. Simpson was released by Cambridge on 9th May 2016. He had played 77 games for Cambridge, scoring 13 goals.

Simpson signed for Exeter City on 25th May 2016 - he had played under Exeter boss Paul Tisdale for England Universities.

Simpson was released by Exeter on 5th June 2018. He then signed for MK Dons on 9th July 2018 on a short term deal. He said "I can definitely bring some experience to the side, we have some really talented players and hopefully my experience can help to bring the best out of them. I'm a versatile, hard-working player who will look to make a big contribution in whatever way I can."

On 15th August 2019 Robbie moved to Chelmsford City. He was appointed as Interim Manager late Janurary 2020 following Rod Stringer's departure. After going unbeaten in 4 from mid-February, without losing at home, "Simmo" was appointed as the Club's new permanent First Team Manager in March 2020.