
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.

Wonderblocks
Secret Agent Chicken (voice) / Put on Boots (voice) · (30 episodes)
2025

Breathtaking
Clare Boxall · (3 episodes)
2024

The Kemps: All Gold
PC Dolan
2023

Dodger Special: Coronation
Minnie Bilge
2023

Boat Story
Other Janet · (4 episodes)
2023

Dodger Special: Bad Egg
Minnie Bilge
2023

Dodger Special: Christmas
Minnie Bilge
2022

Dodger Special: Train
Minnie Bilge
2022

Big Tree City
Kit (voice) · (15 episodes)
2022

Hilda and the Mountain King
Gerda Gustav (voice)
2021

The Kemps: All True
Various
2020
Bumps
Fallon
2020

The Jewish Enquirer
Naomi · (6 episodes)
2020

A Year in the Life of a Year 2019
2020

Worzel Gummidge
Jackie Pudding · (5 episodes)
2019

Mamma Mia! Here We Go Yet Again
Christine Baranski
2019

Horrible Histories: The Movie - Rotten Romans
Birte
2019

Hilda
Gerda Gustav (voice) · (13 episodes)
2018

Disenchantment
Bunty (voice) · (50 episodes)
2018

Thomas & Friends: Big World! Big Adventures! The Movie
Carly / Cowgirls (voice)
2018

Strike
Mrs Niven · (1 episode)
2017

Thomas & Friends: Journey Beyond Sodor - The Movie
Lexi (voice)
2017

Bob the Builder: Mega Machines - The Movie
Mayor Madison (UK) (voice)
2017

Circles
Martine
2016

Digby Dragon
Grizel (voice) · (72 episodes)
2016

The Windsors
Elizabeth I · (6 episodes)
2016

Alan Davies: As Yet Untitled
Self · (1 episode)
2014

Harry & Paul's Story of the 2s
Anne Robinson / Various
2014

The IT Crowd Manual
Self
2014

Phone Home
Astronaut's wife (voice)
2012

The Itch of the Golden Nit
Stressed Alice (voice)
2011
2018: A Year in the Life of a Year

Hey Duggee
Hennie (voice) · (1 episode)
2014

Full English
(6 episodes)
2012

Isle of Spagg
Herring / Fred (voice)
2011

Mid Morning Matters with Alan Partridge
Anthea Turner · (1 episode)
2010
The Stephen K Amos Show
(1 episode)
2010
Sports Mash: Taking the Mic
(11 episodes)
2010

Mongrels
Destiny (voice) · (17 episodes)
2010
Let's Dance for Sport Relief
Herself - Contestant · (1 episode)
2010

Bellamy's People
(8 episodes)
2010
The Wall
(8 episodes)
2008

Headcases
(8 episodes)
2008

10 Days to War
Natalie Fay · (1 episode)
2008
Comedy Shuffle
(1 episode)
2007

The IT Crowd
April · (1 episode)
2006

Tittybangbang
(19 episodes)
2005

The Friday Night Project
Self · (8 episodes)
2005

AD/BC: A Rock Opera
Wise Man
2004

The Mighty Boosh
Townswoman · (1 episode)
2004