The purpose of this study was to test and validate a conceptual model for instructional design that includes a bottom-up design strategy to support the principles of Universal Design adapted for online course development. The concept of Universal Design demands a holistic, bottom-up instructional design model for online course development that integrates technology, accessibility, recent instructional and learning theories, and a participatory postmodern worldview. Given the situation of online learning complying with accessibility requirements and the issues with instructional design addressing diverse audiences and accessibility mandates, it is timely to assess the application of Universal Design to online learning to address the gap of addressing diverse audiences and meeting accessibility mandates. The research question in this study is how and to what extent does a conceptual model incorporating Universal Design principles with other current instructional design practices affect the design, delivery, and accessibility compliance in online higher education courses? This study is intended for faculty, instructional designers, administrators, assistive technology staff, and Web multimedia software vendors associated with higher education. The conceptual model assists these target audiences to design and develop online courses that are accessible without special adaptation or modification. The components of the conceptual model include factors that support newer emergent approaches to instructional design, various programming solutions used in the software engineering field for efficiency, and legal guidelines associated with accessibility. Three rounds of a Delphi Study using an expert panel were used as the basis for this study. A mixed methods concurrent transformative strategy with a qualitative predominant method were used to determine needs, characteristics, and refinements of the conceptual model using model evaluation categories adapted from system dynamics for instructional design. Findings and interpretation of the results culminated in a revised model design that includes heuristics and standards that can evaluate the quality of the learning objects and Web accessibility requirements for each media type and changes in the role of the instructional designer. A significant change in the process of designing instruction is the use of Universal Design for Online Learning (UDOL) Guidelines.