Campbell was one of the founding members of the Bridgespan Group team. While at Bridgespan, she has worked with both foundations and direct service organizations across a variety of sectors including youth development, community development, education reform, and the environment.

Through this work, Campbell has developed a particular expertise in youth development on both the foundation and nonprofit side. In particular, Kelly has focused on business planning for nonprofits, helping nonprofit leaders think through the most effective ways to grow through replication; she is a co-author of the articles "Business Planning for Nonprofits: What it is and why it matters" and "Getting Replication Right: The Decisions that Matter Most."