Mark has collaborated with Smosh on a few occasions. He first appeared as a guest star in Button Bash, and has made a couple of minor appearances since on Smosh and Smosh Games. He was a guest star on You Posted That? and even appeared in Smosh: The Movie as himself. On other channels, he appeared on H3h3's podcast alongside Ian.
- Smosh: The Movie as himself. In the movie, Ian and Anthony are transported into one of Mark's gaming videos. Mark, playing as a murderous monster in the game, proceeds to give chase after Ian and Anthony, intent on brutally killing them.
- H3 Podcast #8 - Markiplier & Ian Hecox (Smosh) with Ian Hecox and H3h3
After dropping out of the University of Cincinnati, Fischbach started on YouTube in September 2011, where he had a first channel with very few views and subscribers. In May 2012, Mark had some issues with monetization that led to him jumping shop to his second and current channel called MarkiplierGame, now simply Markiplier. The channel has since gained well over 21 million subscribers and 10 billion total views over time from collaborations and playing popular horror and indie games. Mark has also done dozens of vlogging and sketch comedy videos, and has raised over $1,000,000 for a variety of charities.
In late 2015, Mark announced that he had to discontinue his fan-favorite series "Drunk Minecraft", in which he plays Minecraft with his friends while getting progressively intoxicated, due to a health condition that could make alcohol fatal. Mark also worked with the sketch comedy team Cyndago until one of the members, Daniel Kyre, attempted suicide in September 2015 died later in the hospital. Mark took a brief hiatus from YouTube.
In late 2016, Mark formed a team of friends to assist in creating higher-quality videos, consisting of his friends Ethan Nestor, Kathryn Knutsen, Tyler Scheid, and his girlfriend Amy Nelson.
- Mark has a golden retriever named Chica.