Although the benefits of consumer involvement in research and health care initiatives are known, there is a need to optimize this for all people with cancer. This systematic review aimed to synthesize and evaluate the application of co-design in the oncology literature and develop recommendations to guide the application of optimal co-design processes and reporting in oncology research, practice, and policy. A systematic review of co-design studies in adults with cancer was conducted, searching MEDLINE, CINAHL, Embase, and PsycINFO databases and included studies focused on 2 concepts, co-design and oncology. A total of 5652 titles and abstracts were screened, resulting in 66 eligible publications reporting on 51 unique studies. Four frameworks were applied to describe the co-design initiatives. Most co-design initiatives were designed for use in an outpatient setting (n = 38; 74%) and were predominantly digital resources (n = 14; 27%) or apps (n = 12; 23%). Most studies (n = 25; 49%) used a co-production approach to consumer engagement. Although some studies presented strong co-design methodology, most (n = 36; 70%) did not report the co-design approach, and 14% used no framework. Reporting was poor for the participant level of involvement, the frequency, and time commitment of co-design sessions. Consumer participation level was predominantly collaborate (n = 25; 49%). There are opportunities to improve the application of co-design in oncology research. This review has generated recommendations to guide 1) methodology and frameworks, 2) recruitment and engagement of co-design participants, and 3) evaluation of the co-design process. These recommendations can help drive appropriate, meaningful, and equitable co-design, leading to better cancer research and care.