Austen was born in Belfast, Northern Ireland. She grew up in Stonehaven, 15 miles (24 km) south of Aberdeen, in the North East of Scotland. She had a generally unhappy and dislocated childhood, including a spell at boarding school, where she was abused. She was an outwardly popular and charismatic child but after suffering years of sexual abuse made worse by her gender dysphoria, she decided to join the British Army to camouflage her real personality.
Austen joined as an officer in the Royal Irish Rangers in 1983, serving in Northern Ireland. She retrained as a TV cameraman in 1987, working for Scottish Television. Her military background saw her dispatched to war zones covering the Gulf War 1, the civil wars in Angola and Afghanistan, and the conflict in Bosnia. She then worked as a director for Scottish and Anglia Television in the 1980 -90's, before leaving to become bureaux chief of Edinburgh Live TV in 1996. In 1997 Hamilton was promoted to editor-in-chief of Live's City TV network by boss Kelvin MacKenzie. Austen resigned from her position at Live TV in 1998, after management changes at their Canary Wharf Headquarters, and took up a senior management position at Granada TV. She has been nominated twice by the British Academy for her television work.
Rejoining the British Army
During 1995, Austen rejoined the Army. As an over-age candidate, she first joined the Territorial Army and then the Regular Army. She joined the Parachute Regiment in 2002, having already passed the stringent selection process at age 35, and went on to attend All Arms Commando Course and elements of Special Forces selection with 22 SAS, becoming a combat survival and a physical training instructor. She served with the Cheshire Regiment and The Highlanders in a variety of command appointments, as well as a number of staff appointments both in the UK and overseas, with a speciality in Information and Psychological Operations. She served on operations in Bosnia, Northern Ireland, the War in Afghanistan and the Iraq War. She returned to the United Kingdom in 2006 and spent a period recovering from two continuous years of operations before taking a position back in Afghanistan with NATO Forces, advising on specialist counter-narcotics operations, from where she was medevacked back to the UK with a serious infection following an IED incident.
Her counsellors confirmed in early 2007 that she had gender dysphoria and from that point she began to live in preparation for surgical intervention. Since then, Austen has had breast augmentation, facial re-construction and finally full gender re-assignment by surgeon Suporn Watanyusakul in early 2008.
She informed her Commanding Officer, Lt. Col. AABR Bruce of Crionaich, of her intention to change gender, and was dismissed from her up-coming post as head of Media Operations in Gibraltar without being granted an interview, to which she was legally entitled. For 14 months, Lt. Col. Bruce refused meetings with her or to comment on the future of her career, despite repeated requests. A senior officer told her, "You've gone from hero to zero in one day". Austen was prevented from appearing at the Parachute Regiment annual officer's dinner. Her family sent her belongings to her with a note saying, "Our son is dead – never contact us again." 
Her lawyers repeatedly sought meetings with the Army to settle the issue out of court. Transgender individuals in the UK are protected under a number of legislative acts, including the Sex Discrimination Act Amendments (1999) and the Gender Recognition Act (2004), which make it illegal to treat a person differently on the grounds of gender alone, with the aim of protecting the rights of trans-people in the work-place. Although other people in the Royal Navy and Air Force have successfully transitioned in the service, as the first officer and first paratrooper, Austen's background caused considerable surprise to the Army, particularly in the light of constant media attention.
The issue was eventually amicably resolved, and Austen resigned her commission. Army policy on trans-gender soldiers has now been formalised to allow soldiers to transition while in service. The Regimental Colonel of The Parachute Regiment wrote to Austen to thank her for her "years of loyal service as an Airborne Officer".".
Austen was the subject of a documentary on Channel 4 (UK) in March 2008 entitled Sex Change Soldier, detailing her experiences as a Paratrooper and undergoing a sex change. This was repeated several times on UK television and sold to a number of other territories, and was the most commented programme on Channel 4 during the month of its original broadcast.
She continues to undertake a number of training and advisory roles on gender issues, including with Lancashire Police. She continues to support the Parachute Regiment by fundraising for Airborne Charities.
She served as a police officer for Strathclyde Police in Glasgow before returning to Afghanistan as a consultant for NATO, working alongside the US forces from Kandahar airbase between 2012 and 2015.
Austen was featured in several UK national newspapers, and has made many television and radio appearances,. She was rumoured to be a possible participant in Big Brother 9 or I'm a Celebrity... Get Me Out of Here!, but did not appear.
Most recently, Austen was reported extensively in the press, particularly in the News of the World, to have secured a £250,000 pay-out for "hurt feelings" from the MoD. She received several threats of violence from serving soldiers because of the attendant publicity of this case, but denied the pay-out and currently has three complaints against various newspapers lodged with the Press Complaints Commission.
The Mail Online  confirmed in a retraction issued, that they "in an article on 31 May may have suggested that Jan Hamilton had sought £250,000 for hurt feelings in her industrial action against the MoD." and that they "are happy to clarify that Ms Hamilton neither sought nor received £250,000 for hurt feelings." Austen insisted that they make a sizeable donation to service charities to compensate for the hurt done to the families of injured service personnel.
- British soldier has sex change – CNN Video
- Cutting Edge – Channel 4
- STV Interview
- Aparthied era SADF forced sex change operations for Gay/Lesbian soldiers
- modoracle.com, Austrian Army takes Soldiers case personal
- Alexandra Genova (2015-11-21). "'The UK's first transgender Army officer full of praise for 'tolerant' Liverpool - where she now calls home". Liverpool Echo. Retrieved 2016-04-08.
- Day, Elizabeth (2007-03-31). "Ian is a captain in the Paras. This week he'll tell the Army he is having a sex change | Mail Online". dailymail.co.uk. Retrieved 2012-04-03.
- CAPT. JAN HAMILTON (2007-10-21). "'A year ago I was Ian, 16 stone with 14-inch biceps, a Captain in the Paras. Today I'm Jan, 11 stone and size 12 | Mail Online". dailymail.co.uk. Retrieved 2012-04-03.
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- Alexandra Genova (2015-11-21). "'The UK's first transgender Army officer full of praise for 'tolerant' Liverpool - where she now calls home;". Liverpool Echo. Retrieved 2016-04-08.
- "Lancashire – Radio Lancashire – Ladies @ Lunch blog". BBC. 2008-04-18. Retrieved 2012-04-03.
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- "Jan Hamilton | Mail Online". dailymail.co.uk. 2008-07-16. Retrieved 2012-04-03.