Johnson attended prep school at Milton Academy before transferring to Tabor Academy and graduating with a Bachelor’s degree from Harvard College in 1954. After a stint in the US Army, he became a research analyst at Fidelity Investments in 1957, a company founded by his father Edward C. Johnson II in 1949. He later became the portfolio manager for the Fidelity Trend Fund in 1960 and ran the famous Fidelity Magellan Fund from 1963 to 1977. He then became president of the company in 1972 and Chairman and CEO in 1977.

In 1965, the US–based Fidelity Foundation was founded by Edward C. Johnson III and his father. The Edward C. Johnson Fund, a $334 million charitable fund, contributes to institutions in the Boston area and beyond.

His other daughter is Elizabeth L. Johnson. In 2012, it was estimated that Elizabeth had a net worth of roughly $2.5 billion.

His son, Edward Johnson IV, is president of family-owned Pembroke Real Estate. The firm manages 6.5 million square feet of office and residential real estate, including the Boston Seaport. In 2012, Edward’s net worth was estimated at $2.5 billion.

His daughter Abigail has taken over the role of CEO of Fidelity Investments and Chairman of Fidelity International in 2014. As of 2012, Abigail owned up to 24% of the shares in Fidelity, had a net worth of $10.3 billion and was ranked 29th on the Forbes 400 rich list.