Formed from a division of the Episcopal Diocese of Massachusetts, it was officially recognized at the organizing convention of November 10, 1901.

At a special meeting on January 22, 1902, Alexander Hamilton Vinton, Rector of All Saints Church in Worcester, Massachusetts, was elected first diocesan bishop.

After the February, 2018 Stoneman Douglas High School shooting, on July 12, 2018, a resolution proposed by Western Massachusetts Episcopal Bishop Douglas John Fisher on a national plan to invest in firearms manufacturers and retailers as a form of shareholder advocacy was approved by the House of Bishops during the 79th meeting of the General Convention of the Episcopal Church in the United States of America in Austin, Texas.

[1] The Episcopal Diocese of Western Massachusetts purchased 200 shares, the minimum holding needed to qualify to formally submit shareholder resolutions, of Springfield, Massachusetts-based firearms manufacturer American Outdoor Brands Corporation (AOBC), the parent company of Smith & Wesson.

[2] The Diocese partnered with the Adrian Dominican Sisters on a shareholder resolution asking AOBC to report to investors regarding the steps they are taking to reduce gun violence.