The 6-foot-3 Reno native said on Friday that he plans to hire an agent in advance of the June 24 draft, ending his collegiate eligibility.
Johnson was a second-team All-Western Athletic Conference selection last season, and averaged 14.3 points, 4.4 assists and 3.7 rebounds in his three-year career.
He ranks fourth at Nevada in career assists with 445 and ninth in scoring with 1,441 points.
Coach David Carter says Johnson is "a great young man who has given Nevada basketball everything he had."
Johnson was named 2008 WAC Freshman of the Year and earned first-team all-conference honors as a sophomore.