In 2009, Mann was elected as county councillor for Wadebridge West, serving briefly on the North Cornwall District Council before it was absorbed by the now unitary authority that is Cornwall Council. In 2013, Mann retained his seat as councillor for Wadebridge West.
In February 2012, Mann resigned as deputy leader of the Conservative group on Cornwall Council in protest at £16 million of public money being used to fund a proposed sports stadium near Truro.
In 2014, Mann met with Conservative MP and Secretary of State for Culture, Media and Sport Sajid Javid in Cornwall to campaign for the continued support for community leisure centres which were at threat of losing funding from the local authority.
In 2013, Mann was named as the Conservative Party's prospective parliamentary candidate for North Cornwall in the run up to the 2015 General Election.
Mann is the Member of Parliament for the constituency of North Cornwall after winning the seat in the 2015 General Election. Scott received 21,689 votes, beating the previous MP, Dan Rogerson, by 6,621 with an approximate 9,000 vote swing. He became the first Conservative MP for the area since 1992, as well as contributing to all six Cornwall constituencies electing Conservative candidates—the first time in over a hundred years. Along with Sarah Newton he took his pledge of allegiance to government in the Cornish language.
In November 2015, Mann introduced a Private Member's Bill to give Town and Parish Councils the power to hold community referendums to alter speed limits. The Bill received its second reading in February 2016 where it was objected to from both sides of the House of Commons and subsequently withdrawn.
Mann campaigned for the United Kingdom to leave the European Union in the 2016 European Union Referendum
In December 2016, Mann was elected (unopposed) to the House of Commons' Environmental Audit Select Committee.
In June 2017, Mann was elected as MP for North Cornwall following a snap General Election, garnering 23,835 votes and a 50.7% share of the vote. His majority also increased to 7,200. Mann was subsequently appointed as a Parliamentary Private Secretary (PPS) for Transport - an un-paid role to assist and support government ministers in the Department for Transport.
Mann was born and grew up in Wadebridge, Cornwall and attended Wadebridge Secondary School. His father grew up in Bodmin, Cornwall; his occupation was in boat construction. His mother grew up in St Kew Highway, Cornwall.
After leaving school at 16, Mann attended St Austell College before becoming a postman for the Royal Mail and was based at the local sorting office in Wadebridge. He is the honorary vice-president of Wadebridge Cricket Club.
On a Summer boat trip in 2016 Mann had to be rescued from drowning by fellow MP Johnny Mercer because he was "ashamed to admit" he couldn't swim. Writing to raise awareness, he said he endangered his life because he was "afraid to own up to something that [he] considered an embarrassment". He has since taken swimming lessons.