[2] Montgomery studied at Victoria University of Wellington, from which he graduated with a bachelor of arts in theatre, film, and media.

[3] To begin his career in comedy, Montgomery moved to Canada in 2010 — first Montreal, and then Toronto, which had more open mic nights.

[11][12][13] After the onset of the COVID-19 pandemic in 2020, the duo did an "emergency season" in which they watched the film Home Alone 3 every three days until their local New Zealand lockdown orders were lifted.

Montgomery's 2014 show Presents a Succinct and Concise Summary of How He Feels About Certain Things won the Billy T Award.

[20] His show Guy Montgomery Doesn't Check His Phone For An Hour played at the Melbourne International Comedy Festival in 2018, which explored his move to New York.

[23] In 2019, Montgomery presented his sixth solo show, I Was Part Of The Problem Before We Were Talking About It, at the Edinburgh Fringe Festival;[24] he described it as "about personal growth and reconciling who I am today with all the iterations of myself I've been throughout the years".

[26] His show My Brain is Blowing Me Crazy premiered in 2023 and won the Fred Award at the New Zealand International Comedy Festival.

[28][29][30] He wanted the show, which aired on weeknights on TVNZ U, to "fill the void that's been left by Eating Media Lunch, Moon TV, [and] Back of the Y".

From U late, where he first met his podcast partner Tim Batt,[32] Montgomery moved into writing for several different comedy shows in New Zealand, such as Jono and Ben at 10.

[36] In 2017, Montgomery and Tim Batt recorded a pilot episode of a The Worst Idea of All Time TV series for YouTube Red, in which they spent five days in a New York City sewer watching Teenage Mutant Ninja Turtles: Out of the Shadows.

Montgomery was a contestant on the 2022 series of the New Zealand reality television show Celebrity Treasure Island, and was the first player to be eliminated.

[42] In 2014, Montgomery won the Billy T Award for his show Presents a Succinct and Concise Summary of How He Feels About Certain Things.