Forsyth started his career at Oxfam as a policy adviser on South Africa during the latter stages of the apartheid era. At Oxfam he helped build campaigns on debt cancellation, Africa, Make Trade Fair and access to medicines. In 1995 he moved to Washington DC to set up Oxfam International, before returning in 1999 as policy and campaigns Director. 
He remained at Number 10 under Gordon Brown, becoming his strategic communications and campaigns director, helping to use new communications strategies to reach the British public on a range of issues, from knife crime to climate change. 
In November 2014 Forsyth's close links to Tony Blair were questioned after the US arm of Save the Children presented Blair with a 'global legacy award' in New York at a glittering 'Illumination Gala' at the Plaza Hotel. The award recognised Blair's 'leadership on international development'.
An internal letter signed by 200 charity staff called for the award to be withdrawn, say it was not only “morally reprehensible, but also endangers our credibility globally”. The letter demanded a review of internal decision-making processes.
- “We consider this award inappropriate and a betrayal to Save the Children’s founding principles and values. Management staff in the region were not communicated with nor consulted about the award and were caught by surprise with this decision,” it said.
Save the Children put out a statement stressing the award was given by the US arm of the charity, not by Forsyth or STC UK. It said the award was presented because of Blair’s work as prime minister on Africa and poverty.
- Christopher Hope Half of Gordon Brown's 'spads' work for charities lobbying Coalition, as Tories condemn 'revolving door' The Telegraph, 15 August 2014, accessed 17 October 2014
- Executive Directors Save the Children, accessed 17 October 2014
- Harriet Sherwood, Save the Children staff furious over ‘global legacy’ award for Tony Blair, The Guardian, Tuesday 25 November 2014 10.27 EST