Previous work for CBBC included gameshow Crush in 2004, Sport Relief Gets Sub’d!, a Sport Relief 2006 show and as co-presenter of Smile, which aired each Sunday on BBC Two until 26 August 2007 and saw him win a Children’s BAFTA for best presenter. He also co-hosted the Doctor Who tie-in programme Totally Doctor Who until it was cancelled after series three in 2007. Harwood was also the Control Voice in an episode of the Doctor Who spin off animated series The Infinite Quest. As an extra, he appeared in the Doctor Who episode “Love & Monsters”, which was first transmitted on 17 June 2006.

In July 2007, Harwood fronted The Sorcerer’s Apprentice, a daily reality series following a group of children learning magic at a Harry Potter-style boarding school. Bear Behaving Badly, a 26-part sitcom starring Harwood and Nev the bear from Smile, was broadcast on BBC One between September and October 2007. In February 2008, Harwood starred as the ‘hidden’ celebrity in an episode of Hider in the House.

From December 2007 to January 2008, Harwood appeared at The Assembly Hall Theatre, Tunbridge Wells as Buttons in Cinderella.

In April 2008, Harwood appeared in a musical version of Beauty and the Beast, as Jangles the court jester, at the Central Theatre in Chatham, Kent.

From December 2008 to January 2009, Harwood starred in Peter Pan at the Pavilion Theatre in Bournemouth. From December 2009 to January 2010, he again starred in Peter Pan, this time at the Grande Theatre in Blackpool.

On 14 November 2009, Harwood made a guest appearance on CBBC series TMi, alongside Little Boots.

On 13 December 2010 it was revealed on the BBC’s Blue Peter that Harwood would be the new presenter on the show, taking over from Joel Defries.

In 2010, Harwood appeared at the Lichfield Garrick Theatre for their Christmas production of Peter Pan, playing the lead role and co-starring with his father, comedian Barnaby.

In December 2013, Harwood played “Peter Pan” at the Theatre Royal in Nottingham, alongside David Hasselhoff and Su Pollard.

In early 2016, Harwood took a break from Blue Peter; he returned later that year. It was announced in August 2017 during the show’s summer break that Harwood would leave the show after six and half years and his final show aired on 14 September 2017 where Harwood would move on from Blue Peter and “onto new adventures”. Harwood announced during his last Blue Peter episode that after 16 years working with CBBC, he would also leave the channel. On his last show he was awarded a Blue Peter Gold Badge, the highest accolade, for his work on the programme. When awarded by co-presenter Chingyanganya, he was described as being “at the very top of the list”.

In August 2017, he appeared as a contestant on Celebrity Masterchef.