Sinclair was born a male, though by late 1971 claims to become clearly aware that personality and feelings were those of a female. However, it was not until 1989 in Britain that she could start to undergo the final surgical stages of gender reassignment surgery.

Sinclaire UKIP posts included Head Office Manager (1999–2001), member of the National Executive Committee (NEC), and Party Secretary under the leadership of Roger Knapman.

Sinclaire stood for the UK Parliament twice as a UKIP candidate: in Medway in 2001 and in Halesowen and Rowley Regis in 2005. At the 2001 general election, she was the party's campaign manager for the three Kent constituencies of Medway, Gillingham, and Chatham & Aylesford.

In 2004, Sinclaire came out as lesbian in a letter to the LGBT newspaper The Pink Paper. She however stated that she had no Desire to be the leader of an LGBT group within UKIP.

During the 2005 general election campaign, Sinclaire stood as the UKIP candidate for Halesowen & Rowley Regis, more than doubling the previous UKIP vote. She was arrested after refusing to leave a public debate, "Queer Question Time" (to discuss issues related to the gay community) but was released without charge a few hours later.

In October 2008, it was reported that Sinclaire briefly met Baroness Thatcher at a Bruges Group dinner. Sinclaire told Thatcher that she would be standing as an MEP candidate for the UK Independence Party in the West Midlands. According to the BBC report, Thatcher replied "Good for you. Never give up, never give up".

Sinclaire enrolled onto the Armed Forces Parliamentary Scheme in October 2009.

The campaign's first roadshow was held in Stoke-on-Trent on 29 July 2010 and visited over 50 towns and cities in the West Midlands alone.

Sinclaire sponsored 13 players during the 2011–12 season from teams across her constituency, ranging from the Conference North to the Premier League. Sinclaire is also a fanatical Liverpool fan and season ticket holder.

On 22 February 2012, Sinclaire was arrested along with three other people; two women aged 55 and 39, as well as a 19-year-old man on suspicion of conspiracy to defraud the European Parliament following an inquiry into an allegation made in 2010, concerning allowances and expenses. Sinclaire denied all the charges, cooperated with the police, and while the investigation was in process would only state that it was tied to a disgruntled employee who was themselves the subject of a similar investigation. On 23 July 2014, she was charged with money laundering, contrary to Sections 327 or 329 of the Proceeds of Crime Act 2002, and misconduct in public office, contrary to Common Law, relating to European Parliament travel expenses, in a period between October 2009 and July 2010.

She is a lover of animals – especially cats, having owned six rescue cats.

In the Court case subsequent to Sinclaire's office manager John Ison having been cautioned by the judge that he was incriminating himself and when it was shown in open court that John Ison was colluding with Nigel Farage, the leader of UKIP, on 11 July 2016, the jury in Sinclaire's trial found her not guilty on all counts.

Alongside her weekly road shows, Campaign for a Referendum created a ‘People’s Petition’ magazine which is in its fourth issue. The magazine gathered cross party support.