While at Jesus College, Cambridge, Montgomery was a member of the Footlights, its amateur theatrical club.
Subsequently, she studied at the Central School of Speech and Drama.
Montgomery built her career as one third of Comedy Theatre Company Population 3, along with James Bachman and Barunka O'Shaughnessy, and she appeared as a roving reporter for the comic television programme The Friday Night Project.
Other television work has included Bo' Selecta!, The Mighty Boosh, and The IT Crowd.
Montgomery has been heard in several Radio 4 programmes, including the radio phone-in spoof Down the Line, Robin and Wendy's Wet Weekends, The Way We Live Right Now, The Museum of Everything, The Department, Another Case of Milton Jones, The Party Line, Harry Hill's Ghost of a Christmas Present, The Pits, the Torchwood story "Lost Souls" and Lucy Montgomery's Variety Pack.
She produced a pilot for her own sketch show pilot for the BBC called The Full Montgomery which went on to run on Radio 4 for two series.
In 2005, Montgomery began writing for and performing in the comedy sketch show Tittybangbang on BBC Three.
The sketch comedy series also stars Debbie Chazen and has had three series, from 2005 to late 2007.
She was in The Armstrong and Miller Show on BBC One, and Bellamy's People on BBC Two.
She has also been on The Law of the Playground and The Wall on BBC Three.
She provided the voice of Destiny in Mongrels.
Montgomery had various roles in The Life of Rock with Brian Pern and Harry and Paul's Story of the Twos.
She was also the voice of Jeanine and other female characters in the Animated Puppetoon children's television series A Town Called Panic.
She voiced for the series Badly Dubbed Porn on Comedy Central.
She has starred in many stage productions, including leads in record-breaking and critically acclaimed Jerusalem with Mark Rylance at the Royal Court in 2009, the 2011–12 revival of Stephen Sondheim's Company at the Sheffield Crucible and Canvas at the Chichester Festival in 2012.
Montgomery appeared in the musical Viva Forever!, based on the music of the Spice Girls.
Spandau Ballet brothers Martin and Gary Kemp return to the BBC for a New Year comedy documentary special. Rhys Thomas OBE has been given unprecedented behind-the-scenes access to their lives for a whole year, and what a momentous one it’s been - with Martin publishing an explosive biography, his two wives, Pepsi and Shirlie, wanting a divorce, and Gary writing Spandau: The Ballet.
Spandau Ballet global superstars Gary and Martin Kemp, their lives, and their careers.
Roman teenager, Atti is forced to join the Roman army when one of his clever schemes falls foul of Emperor Nero. He is sent to "miserable, cold, wet Britain" where "the natives are revolting - quite literally". Things go from bad to worse when Atti is captured by Orla, a feisty teenage Celt desperate to prove herself as a warrior.
Thomas leaves Sodor to fulfil his dream of seeing the world. This heroic quest takes Thomas across deserts, through jungles and over dangerous mountains as he travels across five continents seeing sights he has never seen before.
Join Thomas and his friends in this exciting adventure to the mainland that shows us friendship is more important than being the favorite engine. Can Thomas and the new experimental engines save James and help bring him back to the Island of Sodor?
Bob's team just got BIGGER with the most mega build EVER! Meet new team members Thud, Crunch, and former TV star Ace. They help Scoop, Muck, and Lofty clear the quarry to make room for an exciting new dam and reservoir. However, a rival contractor tries to undermine Bob and it's up to the team to save Spring City. Will they be up to this mega challenge or will it all end up washed away?
This behind-the-scenes documentary features interviews with the creators and cast of the cult comedy "The IT Crowd", plus chats with celebrity fans.
Eleven-year-old Beanie's bland life is changed for ever when he is sent on a mission. Armed only with laser lip-gloss and a pair of blend-in pants he has to save his parents from Evil Stella and return the Golden Nit to its rightful place at the heart of the sun, thereby saving the universe.
An all-singing, all-dancing, star-spangled musical leap around the biblical story of the Nativity, set in 1972. With a comic twist, this familiar story is brought to life through the eyes of the innkeeper. Despairing after a bad year, he contemplates suicide but his attempt is stalled by a voice from above who points out that King Herod is coming to town.