Folan, 24, has signed a three-year deal with the Tigers after spending just six months at the Premier League club.
He made 16 appearances for the Latics last season after a £500,000 January move from Chesterfield, scoring two goals.
"We're delighted to have signed Folan and believe that he's a quality player who will bring attributes that we haven't already got to the squad," Hull boss Phil Brown declared.
"I'm sure the fans are also very excited at the prospect of seeing him play at the KC Stadium."
Plymouth Argyle have signed highly-rated French defender
The France Under-21 international has put pen to paper on a season-long loan with the Pilgrims and manager Ian Holloway believes he has pulled off a major transfer coup.
Southampton have moved to fill the void created by the departure of Kenwyne Jones to Sunderland after signing Middlesbrough's
The Jamaica international has joined Saints on a free transfer after putting pen to paper on a two-year contract.
Watford have signed Argentinean youngster Santiago Aloi on loan from River Plate.
Preston North End have added striker
One player who has exited Deepdale is former Scunthorpe defender Graham Alexander, who formally completed his move to Burnley.
West Brom have lost defender Curtis Davies, who has joined Premier League side Aston Villa on loan with a view to a permanent move.
Fulham defender Gabriel Zakuani has rejoined Stoke City on loan for the remainder of the season.
The 21-year centre-half made nine appearances while on loan at the Britannia Stadium last season and has re-signed for the Potters after failing to break into the first team at the Premier League club.
Stoke have also signed Jamaica international Demar Phillips from Waterhouse, for a "significant" fee.
Queens Park Rangers have signed Mikele Liegertwood in a £900,000 deal from Championship rivals Sheffield United.
Veteran Scottish striker Paul Dickov has joined Crystal Palace on loan from Manchester City.
Also departing City is Danny Mills, who has joined Charlton on loan.
Palace may be welcoming Dickov, but striker Shefki Kuqi has moved to Premier League Fulham on loan.
Joining Mills at The Valley is Reading defender Sam Sodje, who turned down Sheffield Wednesday to make a loan move to the London side.
Leicester City may be without a manager after Martin Allen was sacked in midweek, but their incredible summer of spending goes on - Benfica winger Marco Ferreira has joined on loan.
Scottish Premier League side Motherwell have made a double swoop on the Championship to sign Stephen Hughes and Lewis Grabban.
Leicester midfielder Hughes has put pen to paper on a two-year contract at Fir Park, while teenage striker Grabban joins on loan from Crystal Palace.
Also heading to Scotland is Trinidad & Tobago's World Cup star Chris Birchall, who has moved from Coventry to St Mirren on loan.