Among Adam's other wishes would be to make a biopic about his mother's family life in 1960s East Africa and play his grandfather. As he explains, "I've been told so many amazing stories of their time there and having visited there myself I want others to see what a beautiful place it is. It's all in my head, I just need to write the bugger."

Fond of acting since his early school years, Adam chose the subject for his GCSE studies, then his A Levels at the Strode College in 1999. Inside that school, Adam studied Drama, Film Studies, and English Literature until his 2001 graduation; moment where, as Adam left the school, he then knew that acting was his vocation.

Following his 2005 graduation, Adam's first TV role was as a student during "Slow Bomb", the finale of the action series Ultimate Force starring Ross Kemp. For that work, Adam took his breaks inside a trailer with Simon Lenagan, another guest-star. In that caravan, Adam discussed with his colleague how he wanted to do voice-over. And as the dialogue progressed, Simon encouraged Adam to present his voice reel at Just Voices, a voice-over agency he had co-founded. Which Adam did and since then, the actor started his career in voice-overs; first doing commercials (e.g.: Nintendo, Twix, Berkley, etc.) and corporate voice-overs. Soon came video games, with additional voices in Dragon Age Origins and Dragon Age: Origins – Awakening, then as Fenton Paddock in Lost Horizon (video game), a main role which Adam has, as he explains, "a soft spot for".

With video games, his most notable roles are as Anders in Dragon Age II, as Shulk in Xenoblade Chronicles and Super Smash Bros. for Nintendo 3DS and Wii U, as Tintin for the video game based on the film, The Adventures of Tintin, as Pipin in the Final Fantasy XIV expansion pack Final Fantasy XIV: Heavensward, and as Fenton Paddock in the point-and-click adventure game Lost Horizon. On television, Adam has done guest star acting on the BBC One soap opera Doctors as Martin Rivers (2008), Ben Hardwick (2013), and DC Gerrard Norcroft (2015), performances as Steven Lilwall on the BBC One series New Tricks, and two roles, as Fred and Jack Parsons, for the TV series documentary Dark Matters: Twisted But True on Science Channel. In theatre, Adam has worked on various plays, most notably during 2015 in the role of Stu for a revival of Anthony Neilson's play Stitching at the House of Wolf, and also the role of Dickie Greenleaf for the play adaptation of Patricia Highsmith's The Talented Mr. Ripley at New Diorama Theatre, for which Adam received a Best Supporting Male nomination at the Offies 2016 (The Off West End Theatre Awards). Regarding film, Adam has done main roles on short films like Towers by the filmmaker Azhur Saleem, but also small parts on films like Delicious and as Rupert Drummond on the horror film Scar Tissue. For his work in audiobooks, Adam has also performed narration for Wicked Beloved, a novel by the Novelist Susanne Saville.

After a successful November 2010 audition for an unidentified Nintendo RPG, Adam was offered the role of Shulk, main hero of the video game Xenoblade Chronicles directed by Tetsuya Takahashi through his company, Monolith Soft. Already released in Japan for the Nintendo Wii on 10 June 2010 and set in Europe for 19 August 2011, Adam's job was to participate in Xenoblade's English translation for the 2011 release. Therefore, his recording — helmed by Justin Villier at Side UK — happened over four straightforward weeks; unlike the Dragon Ages' and Tintin's which occurred in separate stages set according to their productions' situations.

Apart from acting, Adam loves to pen down stories; which is, for him, "a good way to stay sharp when I'm not acting." Among those projects came "Bin Men" and "Dogging", two 2011 comedic shorts he shot with Jamie Baughan — his Drama Centre colleague — and the Director Sankar Jayaraman, who filmed him in 2010 on "Bubble Burst".

Of the RPG, Adam described it as "a philosophical game. It explores our place in the universe, do we really exist, God, do we make our own fate or are we on a set course, as well as love, revenge, and friendship." On a personal note, he was proud of Xenoblade and wished the game had gotten more recognition for its merits. About his performance, the actor's work was applauded as he and the entire voice crew got a "Best Vocal Ensemble in a Video Game" nomination in 2013 at the BTVA Video Game Voice Acting Award. Also, as the original Wii game was re-released in 2015 for the New Nintendo 3DS XL, Adam performed as Shulk again for the English version of Super Smash Bros. for Nintendo 3DS and Wii U which came out on October 2014 (Nintendo 3DS) and November 2014 (WiiU).

Like at his audition where he read the game's opening, Adam's performance had to correspond to the character's design and the casting director's desires. In sum, a bold and intelligent young adult who slowly becomes more mature during his quest; with, as Adam was told, "a neutral English voice, not posh sounding, but should sound educated." So Adam applied a tone which, as he says, "is not completely different from my own voice, it's a variation of my own voice. How I was when I was 19, probably!" And to ensure his acting corresponded well to Tetsuya Takahashi's intentions, he also listened to the Japanese voice track, which allowed him to find the proper emotion for his scenes. As the recording team's mission was a faithful and expert localization of Xenoblade's storyline, they also — along with a translator and a Nintendo Producer — had to adjust their translation according to whatever problems in the booth. For instance, if the duration of the character's mouth animation didn't correspond with the voice actor's performance, the crew would either shorten or lengthen the dialogue while keeping fidelity with the original's intent. And if the crew had questions over certain lines or terms, the translator would help them.

Howden returned for Xenoblade Chronicles X in 2015 and Xenoblade Chronicles 2 in 2017, albeit in roles other than Shulk.