Holuša first took up athletics in the steeplechase discipline. He made his international debut at the 2005 World Youth Championships in Athletics, where he finished seventh overall in the boys' 2000-meter steeplechase. He gradually switched from training for the steeplechase to focusing on the 800 meters, for which he qualified for the 2008 Summer Olympics. After many years of racing as an 800-meter runner, he broke out in the 1500 meters when he ran a sub-3:40 result in the men's 1500 at the World Indoor Championships. He subsequently became Europe's 1500-meter indoor champion when he placed first at the 2015 European Indoor Championships.