He worked full-time at a fast food chain. He was lazy and made Natalie do most of the work, even though she also worked full-time. He spent most of his time on the computer or fixing the van, believing when he is off work, he can just chill out.
Apparently, he also swore at Natalie and called her demeaning, vulgar names, and Tyler copied this practice in his disrespectful behavior to Natalie by calling her a big fat b***h. Jo gave Martin a stern talking-to, making it clear that Martin was responsible for this behavior by modeling it to his children (notably Tyler) in the way he treated Natalie. Jo pointed out in the parent meeting that he was 27, not 8.
He is now 38 in 2017.