From his own experience, McGivney recognized the devastating effect on immigrant families of the untimely death of the father and wage earner. Many Catholics were still struggling to assimilate into the American economy. On March 29, 1882, while an assistant pastor at Saint Mary's Church in New Haven, Connecticut, McGivney founded the Knights of Columbus, with a small group of parishioners, as a mutual aid society, to provide financial assistance, in the event of the men's deaths, to their widows and orphans. The organization developed as a fraternal society. McGivney was also known for his tireless work among his parishioners.
The Knights of Columbus was among the first groups to recruit blood donors, with formal efforts dating to 1937 during the Great Depression. As of 2013, the order has more than 1.8 million member families and 15,000 councils. During the 2012 fraternal year, the order donated $167 million and 70 million man-hours to charity.