Productive, equitable, and reciprocal librarian-faculty partnerships are difficult to establish for a range of reasons. This case study describes a long-term collaboration between a Digital Humanities (DH) librarian and a History professor. We trace our two-year partnership from inception and test-run in a small undergraduate seminar to a scaled-up and carefully-designed DH intervention for visualizing spatial and temporal historical arguments in a course with three times the number of students. The article chronicles our process and analyzes the data from the assessment model we designed for reflecting on the efficacy of the intervention and the success of the partnership. Our collaborative model suggests the value of a partnership built over time, based on shared pedagogical values (in this case, student learning outcome-driven pedagogy and scaffolded instruction) and transparent labor practices.