Marcus is introduced as a young hacker (known online by the alias "Retr0") based in the San Francisco Bay Area who is wrongfully flagged with a criminal profile by ctOS 2.0, the electronic mechanism employed to manage the region's infrastructure and surveillance network.

Marcus succeeds in wiping his profile from the system, and joins the hacktivist collective DedSec to raise social awareness about the risks posed by ctOS 2.0 and expose the corruption of its creators, the Blume Corporation.

In keeping with the general shift in tone of Watch Dogs and expansion of its protagonist's abilities, the developers suggested that Marcus' intended playstyle mostly involve stunning enemies using nonlethal weaponry or using hacking skills to create distractions.

Marcus has been the subject of generally positive reception following the release of Watch Dogs 2, with many critics recognizing the character's importance as an unusual representation of African Americans in popular media as well as black people in the video game medium as a whole.

To accomplish this, Ubisoft actively sought out African-American script consultants and actors for their involvement with finding the characters' voices and encouraged improvised dialogue to make them feel real.

Prentiss also acknowledged the positive fan reception to the close friendship between Marcus and a fellow DedSec team member named Wrench, which had been likened to a "bromance".

Marcus hacks into the relevant server and removes incriminating information which is wrongfully placed on his data profile, then flees the facility with the help of DedSec members, who accept him into the collective.

Together with his newfound team members, they celebrate his successful infiltration on a beach near the Golden Gate Bridge, where they unknowingly cross paths with Blume chief technology officer (CTO) Dušan Nemec by chance.

Over the course of the game, Marcus helps DedSec neutralize various threats around San Francisco, as part of their larger goal to bring down Blume by exposing its corruption and other crimes.

Marcus plays a supporting role in Wrench's story arc in Bloodline, a downloadable content expansion for the 2020 title, Watch Dogs: Legion, released in July 2021.

In a preview article about Watch Dogs 2 written for PCGamesN, Kirk McKeand liked that Marcus has more imaginative and varied tastes in music and fashion, exhibits a wider range of emotions, and better gadgets compared to Aiden Pearce.

[15] George Foster claimed that he is the Watch Dogs franchise's best character, and expressed displeasure in an editorial published by TheGamer that Marcus was seemingly left out of the then-upcoming Bloodline DLC for Legion.

[17] Winslow argued that Marcus' overall depiction in Watch Dogs 2 disrupts the typical norms and stereotypes surrounding the vast majority of black video game characters with disadvantaged socio-economic backgrounds, particularly with his atypical visual design and reliance on intellect as opposed to physical brawn.

Writing for Polygon, Tanya DePass said she was impressed by a scene where Marcus interacts with Horatio Carlin, another core DedSec group member who is also African American, while on a visit to the latter's workplace, a prestigious company in the information technology industry located within Silicon Valley.

Wesley Yin-Poole from Eurogamer said it felt "off" to him that he could make the "likeable Marcus Holloway shoot to kill",[5] a sentiment also shared by Stapleton who described the "weird disconnect" as feeling different than roleplaying as a violent criminal like the player characters of Grand Theft Auto V.[11] Stapleton observed that Marcus' personality is the only motivating factor that pushes players toward a non-lethal playstyle of stealth and silent takedowns, as it may become impractical during intense combat situations.