The 30-year-old scored 68 goals in 223 appearances during his first spell at the club before leaving in the summer to join South Korean side Gwangju.
McGinn has since ended his spell with the K League outfit and, on Thursday, the Dons confirmed that the Northern Irishman will be on their books again as of January 1.
"I had a number of options and had some very good options. So I just went back home and relaxed and did not rush into any decision," McGinn told the official website. "But once Aberdeen came calling there was only one place I was going. I am delighted to have everything signed."
"When I was driving up the road this morning it brought back a lot of good memories when I came into Aberdeen. I am over the moon that we got the deal over the line. I have really enjoyed my time off in the last three or four weeks and I am now looking forward to getting going again. I am well refreshed and I am eager to go again."
McGinn will miss Aberdeen's game against Hearts in the New Year and will be eligible to play after the winter break, starting with the trip to Rangers on January 24.