Falconer spent some of her formative years in Bishopbriggs and Milngavie, two towns on the outskirts of Glasgow. After her family relocated to the South of England when she was seven, Falconer moved to Leeds in 1994 to study Spanish and Italian. Whilst studying at university, she also launched her television career. She was offered a contract by ITV to make a documentary and a consumer show on the provision that she left her studies.
Falconer made her television debut in 1994 as a contestant on Blind Date, and later presented BBC Scotland's Big Country, ITV's documentary series "3D" and consumer show We Can Work It Out alongside Judy Finnegan and Jane Harvey. She hosted travel shows, BBC 'Holiday' and ITV's "How to Holiday". She was the main co-host of Entertainment Today from its launch on in 2000 until its end in July 2008 on GMTV.
Her other work includes reporting on I'm a Celebrity... Get Me Out of Here! in Australia for GMTV in 2003, 2004 and 2006, becoming the host of the National Lottery Draws in September 2006 and hosting Cirque de Celebrité in October 2007. She also worked on a show about '24' for Sky One '24 in 24' which she suggested in the first place so she could meet Keifer Sutherland! She has also actively participated in reality shows, winning BBC One's and Sport Relief'sOnly Fools on Horses in 2006. In the summer of 2007 Falconer starred as the 'hidden' celebrity in an episode of the CBBC gameshow Hider in the House. She was a contestant on All-Star Family Fortunes in December 2007. She also appeared on All-Star Mr and Mrs in February 2010. Falconer has also branched out into acting, having had roles in 'Taggart' and in Ecstasy, a film adaptation based on the #1 bestselling book Ecstasy: Three Tales of Chemical Romance by Irvine Welsh.
She won the Sport Relief showjumping competition Only Fools on Horses riding an 8 year old 16 hands mare called J-Lo. Falconer has also posed for photographs in "Arena" and FHM dressed in a black brassiere and underpants. She hosted three series of Fantasy Homes By the Sea. This series is also shown around the world including BBC Canada. Falconer is currently one of the hosts of the popular daytime quiz show Wordplay on Five (previously called Brainteaser).
In June 2009, she was unveiled as the face and body of Adore Moi underwear range by Ultimo.
She guest presented the ITV's This Morning during Holly Willoughby's maternity leave from May to July 2011.On 22, 29 July and 5 August 2011 she returned as a guest presenter.Jenni also starred in the first episode of Ten Mile Menu in July 2010 on ITV1. On 14 March 2013, Global Radio announced that Falconer would join Heart to host a Sunday morning show, replacing Jason Donovan who is taking a break from the network to tour in the musical Priscilla: Queen of the Desert.