Mr. Johnston has been the top producing associate at King Industrial Realty every year since 1988. In 1991, he became a Vice President and in 2008 became Senior Vice President. In 2015, he along with five other King agents purchased the company from its Founder, Charlie King. Since 1992, he has generated leases and sales of over 1,000,000 square feet a year. Among his transactions have been over 600,000 square feet of negotiated build-to-suit projects.

Since joining King in 1984, he has represented national and local firms such as Associated Lerner Shops of America, Borden, Lund International, TRW Automotive, GMAC, Bank of America, All South Warehouse and United Technologies.