Born in Montevideo, Sosa started his career in Danubio at the age of 15, being one of the youngest footballers to play in the Uruguayan First Division. He played for Danubio from 1982 to 1985, when he was transferred to Spain's Real Zaragoza. With this club, Ruben Sosa won the Copa del Rey in 1986, scoring in the final against FC Barcelona. After playing for Zaragoza, Ruben Sosa was transferred to Italy's S.S. Lazio, staying for four years before being sold to Internazionale, where he reached his greatest form as a football player. He was Inter's leading goal scorer in the 1992–93 and 1993–94 seasons, winning the UEFA Cup in 1994. However, the arrival of Dennis Bergkampin the Summer of 1993, led to splits within the Inter camp, and as a result Sosa left Serie Ain the summer of 1995. After years of success in Uruguay, Spain and Italy, Ruben Sosa played for Germany's Borussia Dortmund, winning the Bundesliga title in 1995–96. When he left Borussia Dortmund, he returned to Spain to play for CD Logroñés. After a couple of months playing for the team, Ruben Sosa decided to leave in order to make his dream come true: he wanted to play for his favourite team in Uruguay, famous Nacional. At Nacional, Sosa won the Uruguayan League in 1998, 2000 and 2001, becoming one of the fans' heroes. In 2002, he left Nacional to play in China's Shanghai Shenhua. In 2003, Shanghai won the Chinese Jia-A League title, but the club was stripped of the title in 2013 for match fixing. In 2004, he returned to Nacional, this time as assistant coach, winning the 2005 league title.
Nicknamed El Principito by Uruguayan fans, Sosa was a quick, creative, talented, agile, and powerful left-footed forward, with good skills, control, and explosive acceleration. A diminutive footballer with a stocky physique, he was usually deployed as a second striker, although he was also capable of playing as a main striker, as he was capable of both scoring and creating goals. He was known in particular for his spectacular efforts and thunderous free kicks. A complete forward, who could shoot, volley, dribble, pass with precision, and hold up the ball to create chances for teammates, his attributes made him one of the best strikers in Europe during his prime. He is considered by many to be one of the best Uruguayan forwards of the last thirty years, alongside Luis Suárez, Enzo Francescoli, Carlos Aguilera, Álvaro Recoba, Daniel Fonseca, Diego Forlán, and Rubén Paz.
