Upon graduating from Harvard Business School in 1988, Johnson joined Fidelity Investments - which her grandfather Edward Johnson II founded in 1946 - as an analyst and portfolio manager. In 2001, she was promoted to President of Fidelity Asset Management. In 2005, she became Head of Retail, Workplace, and Institutional Business. She was named president in 2012. In 2014, she became CEO, a role her father had held since 1977, and in 2016 she became chairman as well. In 2018, Johnson introduced cryptocurrency investment at Fidelity, making it possible for institutional investors to trade bitcoin and ethereum.