Minchin was born Louise Mary Grayson in 1968 in British Hong Kong to a Major in the Irish Guards of the British Army. She was educated at St Mary’s School, Ascot, and has a degree in Spanish from the University of St Andrews. She subsequently studied journalism at the London College of Communication.

She started work for Radio 5 Live in 1998, and married David Minchin the same year. She presented many of the station’s main programmes, including Drive and Breakfast. Between September 2003 and April 2012, she was a regular BBC News Channel presenter, initially working alongside Jon Sopel from 7 pm to 10 pm. Minchin then presented the 2 pm to 5 pm slot, also with Sopel, sharing this shift with Emily Maitlis. She was also one of the main relief presenters for the BBC News at One until April 2012.

Louise married David Minchin on 6 June 1998. The couple have two daughters Scarlett and Mia and live near Chester.

Minchin has worked for the Latin American section of the BBC World Service during a year in Argentina, the Today programme, Five and various local radio stations. In 2006 she toured the country in a converted bus meeting England fans as part of the World Cup coverage for BBC News.

In 2006 and 2007, Minchin was a relief presenter on BBC Breakfast while Kate Silverton covered for main anchor Sian Williams. After Williams returned, she continued to co-host the programme, and from May 2009 until April 2012 was the regular weekend presenter of the show. In December 2011 the BBC announced that Minchin would replace Williams as a main presenter of BBC Breakfast along with Bill Turnbull and Charlie Stayt when the programme moved to Salford—the first edition was presented on Tuesday 10 April 2012.

Minchin and Colin Jackson presented the Sunday morning show Sunday Life on BBC One in 2008.

From 21 April 2008 Minchin presented a weekday programme called Missing Live along with Rav Wilding. The programme was shown at 9:15 am after BBC Breakfast on BBC One and ran for 4 weeks. The show returned for a second four-week run from 16 March 2009, and again in March 2010, highlighting both new cases and those previously featured with updates.

In April 2010 Minchin co-presented The One Show for a week alongside Chris Hollins while regular hosts Adrian Chiles and Christine Bleakley were unavailable. She covered again when the show returned in July 2010 for two weeks alongside Matt Baker and one episode with Matt Allwright.

Minchin and Gethin Jones presented the documentary series Crime and Punishment, which began on BBC One on 12 March 2012.

In March 2014 she was awarded an Honorary Doctor of Letters degree by the University of Chester.

She is an amateur triathlete, and qualified as a member of the 2015 Great Britain Age-Group Triathlon Team (45–49 age group). She competed in the standard distance event (1500 m swim, a 40 km bike ride and a 10 km run) at the World Triathlon Championships in Chicago on 19 September 2015. She qualified for the team at the Dambuster Triathlon at Rutland Water on 15 June 2015. She went on to finish 71st out of 78 finishers at the ITU World Triathlon Championships.

In 2016, Minchin competed in Celebrity MasterChef on BBC One finishing second.

In 2019 Louise spoke out on her menopause experiences to raise awareness. She revealed how she had suffered hot flushes on the BBC Breakfast set that lead to them lowering the temperature.