We studied the development, profile, and income mobility among individuals in in-work poverty in Sweden over a period of 30 years using data covering the entire population on a yearly basis from 1987 to 2016. By introducing a more solid work requirement that stretches over more time than the frequently used ‘seven-month rule’, we make sure that the in-work poor person in our study is mainly working. Our results show that the profile has changed: in 1987, the typical in-work poor person was a native-born single woman, but in 2016, they were a married man born outside of Sweden. When modelling income mobility over two 5-year periods, our results show that changes in household composition explain both upward and downward mobility and that it has become harder to change income position. Interpreting the results on a structural level, two conclusions can be drawn. As in-work poverty is no longer female-dominated, the Swedish policy for gender equality has been successful. As it is now closely connected with immigration status, the integration of immigrants into the labour market must improve.