His former side Liverpool also stand to benefit from the deal through a sell-on clause, although there are conflicting figures regarding how much they will receive, with Wales Online claiming it could be as little as £600,000.
Perhaps a bigger issue than the money, is Shelvey himself, who divides opinion, but is still a promising player at 23-years-old.
Both Liverpool and Swansea have cut their losses on him, but Newcastle may be the big winners despite the financial outlay.
It was the Reds who gambled on signing him as a teenager, but Brendan Rodgers lost patience with him and decided to sell him on.
It is up to Shelvey to show that was a big mistake, but he needs to make sure his main emphasis is the team, with the club embattled in a relegation fight.
Liverpool fans have had their say on his move, and there are a number who still rate the England international...
I'd rather that #LFC had kept Shelvey maybe then we wouldn't have the likes of Allen and Milner around our team!!— Dano... (@DanoM7) January 12, 2016
I'd have taken Shelvey for 12mil, think he's quality me #LFC— David Hegarty (@TheEggman83) January 12, 2016
Decent that we're getting money from the Shelvey deal. Bought for £1.7m, sold for £5m & now getting £3.6m. Good business, for a change! #LFC— Dan Roach (@DJDanRoach) January 12, 2016
Still feel we should never have sold Shelvey in the first place too! #LFC— Danny Thorpe (@dannyLFCthorpe) January 12, 2016