Rojas began his professional club with Chilean club Palestino. He then moved to Mexican Club América for the 1975 season. At some point, he signed with Universidad Católica of Chile and was on their roster for the 1981–82 season. In 1983, he moved to the United States where he signed with the Tampa Bay Rowdies of the NorthAmerican Soccer League. He scored eight goals in twenty-nine games that season to lead the team in scoring. On March 23, 1984, the Rowdies released Rojas and he signed a few days later with the Golden Bay Earthquakes. However, on July 10, 1984, the Earthquakes sent Rojas and Hayden Knight to the Chicago Sting in exchange for Ricardo Alonso and Charlie Fajkus. Rojas found himself with a team on the rise as the Sting won the 1984 NASL championship. While he scored only one goal during the regular season, he added two more in the post-season, including one in a 2–1 victory over the Toronto Blizzard in the first game of the championship series. When the NASL folded at the end of the 1984 NASL season, the Sting moved to the Major Indoor Soccer League. Rojas remained with the Sting until it folded at the end of the 1987-1988 MISL season. That summer, he rejoined the Rowdies, who were then playing in the American Soccer League then signed with the expansion Chicago Power of the American Indoor Soccer Association. Rojas remained with the Power through the 1990–91 season, scoring seven goals in twenty-one games as the Power won the AISA championship.
National team
Rojas' career with Chilean national team spanned from 1976 to 1982. That year, he capped his national team career when he was selected to the Chilean team which competed in the 1982 FIFA World Cup in Spain. He was awarded the Chilean National Sportsmanship Award 1978 and 1981
Coaching
Rojas has extensive coaching experience, most of it at the youth level. He acted as an assistant coach while with the Chicago Power. He has also been an assistant coach for both the Libertyville and Vernon Hillshigh school soccer teams. On September 25, 2012, he was named the head coach of the Chicago Soul in the MISL, but was fired on December 2, 2012 after the team went 2-7. He is now coaching at Trevian Soccer Club in Illinois and works with younger players on a daily basis.