Thursday, the Wildcats made things official on their end, with Chris Collins announcing the addition of Turner.
Turner, a 6-foot-7 forward, will sit out the upcoming 2017-18 campaign and have two seasons of NCAA eligibility remaining starting in 2018-19.
"We're very excited to add A.J. Turner into the Northwestern basketball program," Collins said in the announcement. "A.J. brings great experience having played two years in the ACC. He's a long, skilled wing player who will fit in great with the culture we have created here at Northwestern."
Turner started 52 games in his first two collegiate seasons at Boston College. This past season, he was the ACC leader in assist-to-turnover ratio and averaged 8.4 points per game, shooting 42.4 percent from the field and 37.4 percent from behind the 3-point line.
From Big Ten Country, the Michigan-native Turner was ranked by Rivals as the No. 125 recruit in the Class of 2015.