Despite trials with Tottenham, Brentford and Watford as a boy, Robert Rosario drifted into non-league football joining Hillingdon Borough from Harrow in August 1983 at the age of 17. Five goals in nine Southern league starts for Hillingdon alerted scouts from professional clubs and in December 1983, Robert joined Norwich City. An impressive run in the youth side and reserves led to his full debut in a 6-1 victory over Watford in April 1984. Although he scored in his third match for Norwich, he quickly became displaced with the arrival of Wayne Biggins. Robert worked on his game and became a 6ft3 foil to the diminutive Robert Fleck. Despite gaining 4 England under 21 caps, he was never a regular goalscorer for the Canaries. He made a total of 161 appearances (14 as substitute) and scored just 29 goals. One of which though (against Southampton) was the ITV goal of the season 1989/90. Robert also had a period on loan with Wolves in 1985/86 playing twice and scoring one goal.

Robert joined Coventry in March 1991 for £600,000 and played 59 games for the Sky Blues scoring 8 goals. Amazingly Brian Clough signed him for Nottingham Forest in March 1993 for £400,000 in a brave attempt to avoid relegation. Unfortunately the plan did not work and Robert's career was stuck in the reserves of a Division One side whilst Stan Collymore occupied the centre forwards' position. Attempts to break back into the Forest first team, and add to his tally of 26 games (3 goals) were limited by a knee injury which eventually forced his retirement from the professional game in England.

In February 1997, he joined the Carolina Dynamos of the USA's Second Division "The A League" for whom he made 29 appearances scoring 4 goals. In April 1998, he joined another A league side, the Charleston Battery from South Carolina. Robert then returned to the Carolina Dynamo as their Assistant Coach with additional responsibility for youth football. According to their website, he is no longer with the Dynamo but he has applied for the Head Coach position at A-League rivals Hampton Roads Mariners.