In the summer of 1974, while still studying at the University of New Mexico, Johnson decided to work part-time as a handyman, doing various types of work which included simple plumbing, remodeling and even construction jobs. His early success prompted him to start Big J Enterprises in 1976, soon after he graduated. It began as a small one-man operation which suddenly grew to multi-million dollar firm after he secured a contract from Intel for an expansion of their manufacturing facility in Rio Rancho, Sandoval County.
The company, built on a solid platform of worker's welfare and good business ethics, continued to grow in strength. By the time Johnson decided to sell the firm in 1994, following his victory in the gubernatorial election of New Mexico, Big J Enterprises employed over a 1,000 workers. The $38 million deal had a clause in it that prevents the retrenchment of existing workers by the new owners.
After finishing his two terms as Governor in 2002, Johnson rejoined the business sector and currently has interests in three firms in the state – Alpha Security Group Corp (a defense-related investment firm), High Beta (a venture capital firm) and GEJ Enterprises (a consulting firm). Johnson is also a member of the Board of Directors for the Albuquerque Chamber of Commerce.