Atkinson is a former member of the Conservative Party and ran a marketing business for two decades prior to becoming an MEP. As Janice Small, she was a press officer for the Conservatives in the south-east during the 2005 general election and in the 2010 general election, she was the Conservative candidate for Batley and Spen, finishing second, 4,406 votes behind Labour incumbent Mike Wood. She was also director of Conservative Action for Electoral Reform.
Atkinson joined UKIP in 2011, citing David Cameron's failure to produce a referendum on European Union membership. As Janice Atkinson-Small she wrote a column for the Daily Mail.
She was selected as the UKIP candidate for Folkestone and Hythe for the 2015 general election, before being expelled from the party and withdrawn as its candidate due to a 'serious financial irregularity'.
On 16 June 2015, it was announced that Atkinson had joined the newly formed far-right group in the European Parliament, Europe of Nations and Freedom (ENF).
Atkinson is an associate of the American Legislative Exchange Council (ALEC).
During the 2014 campaign it emerged that despite Atkinson's claims – and status as a champion of state selective education – her alma mater, Blackheath Bluecoat School, is not and has never been a grammar school.
It was also reported that, before she joined UKIP, Atkinson was dropped from the 2011 alternative vote campaign following a meeting with undecided Conservatives in which she mentioned "her support for elements of" the British National Party's platform. A few days later Atkinson swore at anti-racism campaigners. The incident followed her call for 'abusive' anti-UKIP protestors to be arrested by the police. A photo capturing the moment was widely reported and went viral on social media. Atkinson, who has described towns in Kent as 'no-go areas' as a result of Eastern European immigration, has defended her position, claiming she marched as part of the Anti-Nazi League in her youth.
In August 2014 she issued an apology after being recorded by a BBC News crew referring to the Thai (or Thai-born) wife of a constituent, who were both UKIP supporters, as "a ting-tong from somewhere", a term used in Thailand for people with mental health problems. The woman and her husband threatened to withdraw from UKIP membership but changed their mind after a personal apology from UKIP leader Nigel Farage. Interviewed on camera later at their home, the woman and her husband said that Atkinson hadn't apologised to them and was quite belligerent. Whilst speaking of Atkinson, Farage said "99% of UKIP members aren't like that and don't hold those views."
In December 2014 it was revealed that Atkinson, whose annual salary as an MEP was around £79,000 per year, owed more than £2,000 in unpaid child support. Her ex-husband claimed this had "caused major hardship for her son and for her family". Atkinson was singled out for criticism as she had previously attacked "feckless families" who have more children than they can afford.
On 19 March 2015 Atkinson was suspended from the party following "allegations of a serious financial nature." The Sun published a secret recording in which Atkinson's chief of staff, Christine Hewitt, spoke to a staff member at a restaurant in Margate and asked them for a fraudulent invoice, inflating the bill to over three times the cost of the £950 meal. On the recording Hewett was heard to say “we overcharge them slightly, because that’s the way we repatriate it.” The following day the police were reported to be investigating.
On 23 March Atkinson was expelled from UKIP for "bringing the party into disrepute". No legal action was taken against Atkinson, but Hewitt pled guilty to fraud and was given a suspended jail sentence.
In the aftermath of the 2017 Manchester Arena bombing, Atkinson called for death penalty for those convicted of terrorism.