This study investigates how working memory (WM) capacity and L2 linguistic knowledge affect L2 literal and inferential reading comprehension, considering the presence or absence of background knowledge. Eighty upper-intermediate to advanced adult English learners participated, completing tasks to assess WM capacity, background knowledge, L2 linguistic knowledge, and reading comprehension (both literal and inferential). Stepwise regression analyses revealed that WM capacity had a stronger influence on both literal and inferential comprehension when background knowledge was absent. For literal comprehension, L2 linguistic knowledge was the sole predictor when background knowledge was present, while WM capacity dominated in its absence. Inferential comprehension was consistently predicted by WM capacity, regardless of background knowledge. These findings indicate that WM capacity and L2 linguistic knowledge influence L2 reading comprehension differently depending on background knowledge and the type of comprehension. Implications include incorporating WM training into L2 reading instruction and employing diverse WM assessment methods to measure WM independently of L2 linguistic proficiency.