Mark is an edgy "rebel without a cause"-type hunk who dates and later elopes with Becky, much to the Conners' consternation. He is played by the late Irish actor Glenn Quinn. Despite Mark's tough-guy image and frequent disregard of authority, he is rarely seen to engage in actual criminal activity, except for the episode where he is intoxicated at the Lobo Lounge and punches through the glass of the bar's jukebox, and another time when he punches out Becky's verbally abusive boss at the Buy & Bag market, and when he moons photographers swarming the house after the Conners win the lottery. Mark is strongly disliked by Roseanne for his condescending attitude toward her; however, she eventually treats him with at least token respect, realizing that he is sometimes even more comitted to his marriage than Becky is.
Although he tends to be idiotic in intellectual levels, Mark has basic street-smarts, understands mechanics, and can be very shrewd at times. Since he was thrown out of his hous by his alcoholic parents at age 16, he has always valued his ability to get by without assistance, which is why he often snubs the Conners; however, he later admits that he is grateful for the moral support and knowledge they have given him and Becky over the years. Becky recognizes Mark's intelligence shortcomings, but loves him for his determination and devotion- although they sometimes have fights, mostly over his inabiltiy to understand the concept of feminism because of his 'macho' attitude. DJ often looks at Mark as a role model (although this backfires badly on him once when he asks Mark for advice on girls) and the two of them sometimes band together to torment David. Darlene, on the other hand, tends to treat Mark with constant disdain; however, the concluding episode reveals that she has actually been dating him all along 'in real life'.
Dan initially dislikes Mark also but respects Mark's work ethic and hires him as a mechanic both at his bike shop and his truck-inspection office. Mark's personality changes drastically over the course of his duration on the series, ultimately proving himself to be a caring, responsible, though dim-witted, husband and brother - as a result Roseanne and the family grows fond of Mark, though they still get amusement out of mocking his stupidity, and taking advantage of him: such when the young couples played a game of Scrabble, Mark won the game by using the word 'oxygen', they lie to him saying that oxyen is not a real word. His devotion to Becky is often stronger than hers for him, since she is usually the one who initiates split-ups between them when they do happen. He has a younger and much more intelligent brother, David , who dates (and later marries) Darlene and also two little sisters, Lisa and Nikki, who are much younger and appear briefly in the episode "No Place Like Home for The Holidays" from the 5th Season and are mentioned later to have moved with their dad when their parents divorced. Mark often makes fun of David for his sensitivity and lack of traditional masculine traits; David was once able to recite a long list of ways in which Mark unnecessarily tormented him just to prove his superiority. However, Mark understands that David, who remained at the Healy house until Season 5, suffered physical and verbal abuse from one (and probably both) of their parents after Mark left home, and he is at times protective of his younger bother. he loyally serves as David's best man at his wedding and is there for him when Darlene goes into early labour, almost losing her daughter. Mark's opinion of his harsh parents is far lower than David's, although he appears to have a slight connection to their father.
At the end of season 9, it is revealed to the audience that Becky and Mark are expecting their first child; with this knowledge, Mark displays surprising sensitivity when he visits his newwborn neice, Harris, claiming, "This dad thing is going to be amazing".