O’Neill joins the Lions from Dutch club Excelsior Rotterdam, where he made 11 appearances between the senior and U21 sides in 2017-18. O’Neill scored one goal and made 31 appearances in 2016-17 for Dutch club NAC Breda, which he led to promotion to the Eredivisie.
O’Neill began his professional career in 2012 with the Colorado Rapids as a Homegrown prior to moving overseas. He scored one goal and made 57 appearances across all competitions for the Rapids from 2012 to 2015.
A native of Middleton, Ireland, O’Neill is a United States citizen and will not fill an International Roster Spot. O’Neill made 15 appearances with U.S. youth national teams from 2013 to 2015. O’Neill was most recently called into the U.S. senior national team camp in January 2015.