Harland was appointed HD's Executive Director in 2011. In 2018, he publicly announced that the Basque armed group ETA had dissolved itself as the final step in a long-running process to bring an end to violence in the Basque country.

In 2022, Harland and HD were cited as an initiator of the UN-brokered deals to ease the global food crisis by facilitating agricultural exports from Russia and Ukraine. HD was awarded the Carnegie Wateler Peace Prize for 2022 ""for its more than 20-year track record in ending armed conflict and for its patient, creative and discreet approach”. Harland also sits on the UN Secretary-General's High-Level Advisory Board on Mediation and on the Scientific Advisory Board of the Robert Koch Institute Centre for International Health Protection (ZIG). Prior to that, Harland was adjunct professor at the Johns Hopkins School of Advanced International Studies (SAIS) and Chair of the World Economic Forum Global Agenda Council on Conflict Prevention. Before joining HD, Harland was director of the Europe and Latin America Division of the United Nations Department of Peacekeeping Operations (2006–2011), where he managed the end of the UN transitional administration in Kosovo.