Jamie made his debut for the GB & NI team at a Junior International in Salamanca, Spain, in 1991, winning the 200m and breaking the Welsh record in that race. Baulch then changed his distance preference becoming a 400 metres specialist. Baulch particularly excelled at running the distance indoors (where races are usually run on 200m tracks rather than outdoor tracks which are 400m long). He won the 400m gold medal at the World Indoor Championships in 1999, and also claimed silver and bronze medals at the event in 1997 and 2003.
Baulch was a member of the British 4 × 400 m relay team which finished second in the 1997 World Championships. However, on 7 January 2010, it was announced the British team are to be awarded the gold medal as they were beaten by a United States team which included Antonio Pettigrew, who subsequently admitted to having taken performance-enhancing drugs, thus disqualifying the US team. Baulch received his World Championship gold medal in May 2010 and, although he was happy, he said: "It would have been great to have been in front of 80,000 people up on the rostrum...nothing can replace that. This is a second best unfortunately, but it's nice to be recognised".
In 1993 he ran a Welsh record 46.50 at Sheffield in his first individual race at the distance since 1990, and he made a breakthrough in 1995 when he progressed to 45.14.
In 1996 he ran a 44.19 second leg for Britain's Olympic silver medal team that set a European record, and set his fifth Welsh record with 44.57.
In 1997 he set Welsh indoor records at 46.36 and 46.13 before smashing Todd Bennett's 12-year-old UK and Commonwealth indoor record of 45.56 with 45.39 at the UK Trials and then took the World Indoor silver behind Sunday Bada (Nigeria). Later he made the World final outdoors with a season's best 44.69 in the semis and ran a 44.08 third leg on the British silver-medal relay team.
After a slow start to the 1998 season he was back in good form at the Commonwealth Games.
In 1999 he won all of his five competitions at 400m, including taking the gold medal at the World Indoor Championships in Maebashi, Japan and running a best time of 45.60 in Birmingham.
Outdoors he had a best of 44.82 in Lausanne, which he followed with a clear win at the AAAs in 45.36. At the World Championships he had four individual runs in the low-45s, again making the final, and ran a 44.24 anchor leg for the British team that went out in the heats of the 4 × 400 m.
In 2000 he won over 400m at the European Cup and had a season's best of 45.06, but he had a disappointing Olympic Games, going out in the heats of the 400m in 46.52, although producing a final leg of 44.65 to ensure that Britain made the final of the 4 × 400 m.
He was selected as captain of the British team at the 2001 World Indoors, but had to withdraw through injury and struggled for form in the summer, with a season's best of 46.15 in the heats at Edmonton, where he ran an encouraging 44.4 second leg for the British team in the final of the World 4 × 400 m. With an individual best of 46.01, he was again seen to best effect in relays in 2002, with a third leg of 45.1 to help Britain to victory in the European Cup 4 × 400 m and a third leg of 44.5 for the Welsh team that took the silver medal at the Commonwealth Games in a race against England.
He came back to form in 2003 with two bronze medals at the World Indoors, when he ran 45.99 to share the individual bronze medal with Paul McKee and in the relay. He ran a solid third leg for the British 4 × 400 m team at the European Cup, but had a disappointing outdoor season with a best of 46.43.
Baulch left coach Linford Christie in a bid to revive his athletics career, moving to Atlanta with new trainer Innocent Egbunike of Nigeria, a 4 × 400 m bronze medallist at the 1984 Olympics and a silver medallist in the individual 400m at the world championships in 1987.
In 1999 and 2000, Baulch hosted the British children's series Energize! He has also appeared on A Question of Sport, and finished third in the BBC programme Superstars in 2003. He was a trainee ranger in Safari School, broadcast in January–February 2007. Baulch became part of a circus act on Cirque de celebrite
After his retirement from athletics in 2005 Baulch set up several different businesses including 'definitive', his sports management company that manage sports personalities including Shane Williams, Dai Greene and Tasha Danvers. He also owns a sports memorobillia company named 'Authentic Sports' and a company, 'Jamie Baulch Academy', which sends sports personalities into schools to encourage children to become more involved in sport.
Baulch is also known to be actively involved with Jaguar Cars.
In January 2008 Baulch was appointed a sprint coach for the Bradford Bulls Rugby League Club.
Baulch also became a squad member for the Welsh touch rugby team in 2010 which won the European cup later that year.Jamie Baulch has been involved with a local charity called Ty Hafan a children's hospice.
Baulch also competed in race against a racehorse raising money for Barnardos.
Baulch also ran in the London Marathon in 2011 raising money for Barnardos.
Baulch excelled as a trampolinist in his youth, and won a silver medal at the Welsh Schools Trampoline Championship in 1991.
Baulch was born in Nottingham, but raised by adoptive parents in Risca, near Newport, Wales. Baulch is mixed race, his biological parents being a white English mother and a black Jamaican father. In 2014 Baulch made a TV documentary for the BBC, Jamie Baulch: Looking For My Birth Mum, where he tracked down and was reunited with his birth mother.