She is now known best as 'Knuckles Ritchie' on the drive home radio show Kate, Tim & Marty on Nova, where she runs her own segment called "Kate's Korner" and is best known for her attempts at comedy or "zingers" which is accompanied by the Jerry Seinfeld theme.
Ritchie was born as Katherine Leigh Ritchie. Her parents are Heather and Steve, and she has three younger siblings, Rebecca, Stuart and Susan. Ritchie attended Campbelltown North Public School and Hurlstone Agricultural High School – the latter a New South Wales agricultural and selective school.
Ritchie was cast as Molly, the child lead in the 1986 Nine Network–PBL mini-series Cyclone Tracy, starring Chris Haywood and Tracy Mann. She started working with Home and Away in 1987, at age 8. Production began in July 1987 (shortly before her ninth birthday) and it premiered on the Seven Network on 17 January 1988. In 2006, Ritchie played "Nicole" in the ABC film Stepfather of the Bride. Whilst promoting Home and Away in the United Kingdom in 2006 with Mark Furze and Jodi Gordon, Ritchie appeared on The Friday Night Project and Loose Women, and appeared on interviews for Five and Five Life.
In 2006, Ritchie was a contestant on the celebrity singing competition It Takes Two, partnered with Troy Cassar-Daley. The pair placed fourth in the competition. She co-hosted the second series of It Takes Two with Grant Denyer in 2007. In 2007 Ritchie joined Nova radio to co-host the drive show with comedian Akmal Saleh, replacing Matthew Newton. She was replaced in May by New Zealand comedian Cal Wilson.
In September 2007, Ritchie announced that she would be leaving Home and Away in mid-December. Her final scenes were filmed on 13 December 2007, and she last appeared on Australian screens as Sally Fletcher on 3 April 2008. Her UK demise with the same episode occurred not long after the Australian, with her departure being screened on UK terrestrial television on 12 May 2008.
On 14 January 2008, Ritchie began work on the Nova 91.9 breakfast show with Merrick & Rosso. Shortly after the 2008 Logie Awards Ritchie did an interview with Rove McManus on Network Ten, her first interview with another network since leaving Home and Away, and her first television appearance since leaving the show. On 16 October Ritchie appeared on pay-TV, on The Merrick & Rosso Show.
In November, it was revealed that Ritchie would appear in the second series of Underbelly, as Judi Kane, the wife of slain 1970s standover man Les Kane. The series screened in 2009. This was her first TV drama role since leaving Home and Away. Throughout 2009, Ritchie continued her radio role on the Merrick & Rosso and Kate Ritchie Show.
In 2009 Ritchie became the face of Vaseline. It was announced on 7 November 2009 that Ritchie would host the 2009 ARIA Awards on 26 November, alongside actor and fellow Underbelly cast member Gyton Grantley.
On 10 November 2009, Ritchie announced she would be leaving Nova 96.9's breakfast team and returning to acting. In January 2010 it was announced that Ritchie had been cast with a lead role in Nine's new police drama Cops L.A.C. The series did not rate well and was cancelled after the season finale.
In 2012, Ritchie narrated the Australian version of the reality series Don't Tell the Bride, which aired on Ch-10. In early 2013, it was announced that Ritchie was returning to Home & Away, reprising her role as Sally Fletcher.
In 2013, Ritchie announced via Twitter that she would be hosting the Nova FM drive show with Tim Blackwell and Marty Sheargold in 2014, following the departure of Meshel Laurie, who went on to host Breakfast on Nova 100 in Melbourne.
On 25 November 2015, Ritchie became the Godmother of the Cruise liner Pacific Eden, which is from the P&O Fleet.
In 2016 Ritchie released a children's book illustrated by Hannah Sommerville called I Just Couldn't Wait To Meet You.
In June 2016 Ritchie was announced as the brand ambassador for QV Skincare. Ritchie will host the retrospective 50th anniversary of Play School in July 2016.
Ritchie started dating St George Illawara Dragons player Stuart Webb in 2008. On 9 September 2009, it was announced that they were engaged. On 25 September 2010 Ritchie married Webb in a countryside outdoor wedding at Quamby Estate in Tasmania.
Shortly after her wedding, the weekly magazine Woman's Day ran what it claimed to be an exclusive cover story on the event. ABC-TV's Media Watch revealed that the article had been a fabrication, as in reality, Ritchie and Webb had wanted their wedding to be kept private and had not allowed any media to attend. A photograph purporting to be of Ritchie in her wedding dress was actually one taken of her at an awards evening earlier that year and photo-shopped over an image taken from the wedding venue's website. The article, which the magazine claimed to have been written by an insider who attended the wedding, was mostly fabricated, containing errors including a mention that actor and Ritchie's Home & Away co-star Ray Meagher was present whereas in reality, the actor was in the UK at the time doing panto.
In March 2014, Ritchie announced that she was pregnant with her first child. On 17 August 2014, Kate gave birth to daughter, Mae.