Born in Boston, Massachusetts, Pellagrini began his professional baseball career in 1938 and worked his way up through the minor leagues before being acquired by the Red Sox in September 1941, but spent 1942–1945 in the United States Navy, serving in the Pacific Theater of Operations, during World War II.

Traded to the Browns after the 1947 season in the deal which brought Vern Stephens to Boston, he enjoyed his most consistent play in St. Louis, appearing in 184 games over two years and batting .238 in both campaigns.

[1] Pellagrini went on to become the baseball coach at Boston College from 1958 to 1990 (although he missed the 1969 season due to illness), compiling a record of 359–345–6.

In 1960, his Eagles defeated Connecticut and Holy Cross in the regional tournament to advance to the CWS, where they beat Northern Colorado before losing to USC and Oklahoma State.

An opening-round CWS win against Rider was followed by losses to eventual champion Arizona State and Houston, the latter a 3-2 decision in 13 innings, ending the Eagles' play.