Smart averaged 11.1 points, 3.3 rebounds and 2.4 assists, while the 6-foot-7 Williams averaged 7.0 points and 5.4 rebounds. Neither player is a top 100 prospect in ESPN's draft rankings.
Smart's recruitment by coach Will Wade became the focus of an investigation after FBI wiretaps reportedly picked up Wade saying he made a "strong-ass offer" to a person associated with Smart. Wade has been indefinitely suspended.
Smart sat out the regular-season finale against Vanderbilt after the news first emerged. But school officials said they found no wrongdoing by Smart, and he returned to play in the SEC and NCAA tournaments.
"Being at LSU has been a great experience for me and I will cherish these moments forever," Smart said in the Instagram post. "After meeting with my family and coaching staff, I have decided to enter the NBA draft to pursue my dream as a professional basketball player. ... In my heart, I will always be a Tiger."
Under a new rule, players who have declared for the draft have until May 29 to decide if they want to withdraw from the process and return to college.