National guidelines recommend that maternity systems provide patient-centered access to immediate postpartum long-acting reversible contraception (ie, insertion of an intrauterine device or implant during the delivery hospitalization). Hospitals face significant barriers to offering these services, and efforts to improve peripartum contraception care quality have met with mixed success. Implementation toolkits-packages of resources and strategies to facilitate the implementation of new services-are a promising approach for guiding clinical practice change. This study aimed to develop a theory-informed toolkit, evaluate the feasibility of toolkit-based implementation of immediate postpartum long-acting reversible contraception care in a single site, and refine the toolkit and implementation process for future effectiveness testing. We conducted a single-site feasibility study of the toolkit-based implementation of immediate postpartum contraception services at a large academic medical center in 2017 to 2020. Based on previous qualitative work, we developed a theory-informed implementation toolkit. A stakeholder panel selected toolkit resources to use in a multicomponent implementation intervention at the study site. These resources included tools and strategies designed to optimize implementation conditions (ie, implementation leadership, planning, and evaluation; the financial environment; engagement of key stakeholders; patient needs; compatibility with workflow; and clinician and staff knowledge, skills, and attitudes). The implementation intervention was executed from January 2018 to April 2019. Study outcomes included implementation outcomes (ie, provider perceptions of the implementation process and implementation tools [assessed via online provider survey]) and healthcare quality outcomes (ie, trends in prenatal contraceptive counseling, trends in immediate postpartum long-acting reversible contraceptive utilization [both ascertained by institutional administrative data], and the patient experience of contraceptive care [assessed via serial, cross-sectional, online patient survey items adapted from the National Quality Forum-endorsed, validated Person-Centered Contraceptive Counseling measure]). In the implementation process, among 172 of 401 eligible clinicians (43%) participating in surveys, 70% were "extremely" or "somewhat" satisfied with the implementation process overall. In the prenatal contraceptive counseling, among 4960 individuals undergoing childbirth at the study site in 2019, 1789 (36.1%) had documented prenatal counseling about postpartum contraception. Documented counseling rates increased overall throughout 2019 (Q1, 12.5%; Q4, 51.0%) but varied significantly by clinic site (Q4, range 30%-79%). Immediate postpartum long-acting reversible contraception utilization increased throughout the study period (before implementation, 5.46% of deliveries; during implementation, 8.95%; after implementation, 8.58%). In the patient experience of contraceptive care, patient survey respondents (response rate, 15%-29%) were largely White (344/425 [81%]) and highly educated (309/425 [73%] with at least a 4-year college degree), reflecting the study site population. Scores were poor across settings, with modest improvements in the hospital setting from 2018 to 2020 (prenatal visits, 67%-63%; hospitalization, 45%-58%; outpatient after delivery, 69%-65%). Based on these findings, toolkit refinements included additional resources designed to routinize prenatal contraceptive counseling and support a more patient-centered experience of contraceptive care. A toolkit-based process to implement immediate postpartum long-acting reversible contraceptive services at a single academic center was associated with high acceptability but mixed healthcare quality outcomes. Toolkit resources were added to optimize counseling rates and the patient experience of contraceptive care. Future research should formally test the effectiveness of the refined toolkit in a multisite, prospective trial.