[4] In 2003 he was in charge of negotiation between Costa Rica and Nicaragua for the Procuenca del Río San Juan Project and as a researcher of the Program of High Public Management of INCAE in 2004.
He joined the Citizens' Action Party in 2005 and served as an advisor in Deputy Ruth Montoya Rojas' office.
During his tenure as interim chancellor, he was responsible for leading the III Summit of CELAC hosted by Costa Rica.
[5][6] He assumes the position of Costa Rican ambassador in Managua, Nicaragua, as of June 8, 2016 after the previous holder, Javier Sancho Bonilla, retired.
Trejos has also served as professor of theory of the state and international affairs at the Universidad Latina de Costa Rica.