Recent evidence suggests that constraints can facilitate creative thinking rather than hinder it. This research tested how individual differences in working memory capacity (WMC) affect the creativity of ideas generated under conditions of low and high constraint. Participants generated short sentences with either low or high constraints placed on the choice of initial letters used. Under the high-constraint condition, participants were less likely to successfully produce sentences but the sentences were judged as more creative. There was an interaction between constraint condition and working memory capacity such that WMC and creativity were positively associated in the low constraint condition, but not in the high constraint condition. An examination of strategy reports also indicated that higher WMC participants may have made better use of strategies which were related to higher creativity in the low-constraint condition. This research adds to findings that constraints can be beneficial for creativity, and is consistent with suggestions that WMC enhances efficient search and retrieval from long-term memory and use of strategies.