The 2021 UK summer transfer window commenced on Tuesday the 1st June 2021 and concluded on Tuesday the 31st August 2021 and there has been a significant amount of activity involving Irish players which we detail below. Most notable is the £12 million signing of 20 year old centre back Nathan Collins by Burnley from Stoke City while Manchester City goalkeeper Gavin Bazunu is on a season long loan at League One Portsmouth. Mick McCarthy at Cardiff City has made two significant acquisitions in senior international striker James Collins from Luton Town and U21 centre back Mark McGuinness from Arsenal. Nineteen year old Tottenham Hotspur striker Troy Parrott has gone on a season long loan deal to League One MK Dons. James McCarthy has joined Glasgow Celtic on a four year deal following his release by Crystal Palace. Following a falling out with his Stoke City manager, James McClean has joined League One Wigan Athletic on a one year contract for an undisclosed fee. Twenty three year old Liam Scales has joined Glasgow Celtic from Shamrock Rovers on a four year contract for a fee believed to be €600,000. Midfielder Jayson Molumby has joined West Bromwich Albion on a season long loan from Brighton & Hove Albion with an option to make the move permanent. Another midfielder Conor Hourihane has joined Sheffield United from Aston villa on a season long loan. Deadline day moves include season long loans for senior international Harry Arter from Nottingham Forest to Charlton Athletic, U21 internationals Conor Coventry from West Ham United to Peterborough United and Lee O’Connor from Glasgow Celtic to Tranmere Rovers where he spent last season on loan.
| Name | From | To | Details |
| Val Adedokun | Dundalk | Brentford | Undisclosed |
| Harry Arter | Nottingham Forest | Charlton Athletic | Season Loan |
| Padraig Amond | Newport County | Exeter City | Season Loan |
| Gavin Bazunu | Manchester City | Portsmouth | Season Loan |
| Jack Bonham | Gillingham | Stoke City | 1 Year Deal |
| Jamie Bowden | Tottenham Hotspur | Oldham Athletic | Season Loan |
| Robbie Brady | Burnley | End of Contract | |
| Courtney Brosnan | West Ham United | Everton Ladies | 1 Year Deal |
| Dennis Cirkin | Tottenham Hotspur | Sunderland | 3 Year Deal |
| Jack Clarke | Aston Villa | End of Contract | |
| Trevor Clarke | Rotherham United | Bristol Rovers | 1 Year Deal |
| James Collins | Luton Town | Cardiff City | Undisclosed |
| Nathan Collins | Stoke City | Burnley | £12 million |
| Dylan Connolly | St Mirren | Northampton Town | 2 Year Deal |
| Conor Coventry | West Ham United | Peterborough Utd | Season Loan |
| Ryan Delaney | Bolton Wanderers | Morecambe | End of Contract |
| Gary Dicker | Kilmarnock | Brighton & Hove A | U23 Player/Coach |
| Colin Doyle | Hearts | End of Contract | |
| Jake Doyle-Hayes | St Mirren | Hibernian | 2 Year Deal |
| Aaron Drinan | Ipswich Town | Leyton Orient | 2 Year Deal |
| Courtney Duffus | Bromley | Morecambe | 2 Year Deal |
| Jimmy Dunne | Burnley | QPR | 3 Year Deal |
| Zack Elbouzedi | Lincoln City | AIK Solna(Sweden) | 3 Year Deal |
| Will Ferry | Southampton | Crawley Town | Season Loan |
| Kian Flanagan | Crystal Palace | Barnet | |
| Alex Gilbert | Brentford | Swindon Town | Season Loan |
| Stephen Henderson | Crystal Palace | End of Contract | |
| Conor Hourihane | Aston Villa | Sheffield United | EoS Loan |
| Ryan Johansson | Sevilla | Fortuna Sittard | Season Loan |
| Alan Judge | Ipswich Town | Colchester United | 2 Year Deal |
| Fiacre Kelleher | Wrexham | Bradford City | 2 Year Deal |
| Liam Kelly | Feyenoord | Rochdale | 2 Year Deal |
| Richard Keogh | Huddersfield Town | Blackpool | 1 Year Deal |
| Peter Kioso | Luton Town | MK Dons | Season Loan |
| Bosun Lawal | Watford | Glasgow Celtic | 3 Year Deal |
| Ian Lawlor | Doncaster Rovers | Dundee | 2 Year Deal |
| Kameron Ledwidge | Southampton | End of Contract | |
| Conor Masterson | QPR | Cambridge United | Loan to January |
| Charlie McCann | Manchester United | Glasgow Rangers | £750,000 3yr deal |
| James McCarthy | Crystal Palace | Glasgow Celtic | 4 Year Deal |
| James McClean | Stoke City | Wigan Athletic | 1 Year Deal |
| Mark McGuinness | Arsenal | Cardiff City | 3 Year Deal |
| Shane McLoughlin | AFC Wimbledon | Morecambe | 1 Year Deal |
| Paul McShane | Rochdale | Manchester United | U23 Player Coach |
| Jayson Molumby | Brighton & HA | West Bromwich Alb | Season Loan |
| Brian Barry Murphy | Rochdale | Manchester City | Dev. Squad Manager |
| Corrie Ndaba | Ipswich Town | Salford City | Season Loan |
| Glory Nzingo | St Patrick’s Ath | Reims (France) | |
| Michael Obafemi | Southampton | Swansea City | 3 Year Deal |
| Jake O’Brien | Cork City | Crystal Palace | Undisclosed |
| Darragh O’Connor | Leicester City | Motherwell | 1 Year Deal |
| Lee O’Connor | Glasgow Celtic | Tranmere Rovers | Season Loan |
| Thomas O’Connor | Southampton | Burton Albion | 2 Year Deal |
| Ademipo Odubeko | West Ham United | Huddersfield Town | Season Loan |
| Eunan O’Kane | Leeds United | End of Contract | |
| Corey O’Keeffe | Mansfield Town | Rochdale | January 2022 Loan |
| Armstrong Okoflex | Glasgow Celtic | West Ham United | 2 Year Deal |
| John O’Sullivan | Morecambe | Accrington Stanley | 3 Year Deal |
| Troy Parrott | Tottenham Hotspur | MK Dons | Season Loan |
| Anthony Pilkington | East Bengal | Fleetwood Town | 1 Year Deal |
| Alan Power | Kilmarnock | St Mirren | 1 Year Deal |
| Louise Quinn | Fiorentina | Birmingham City L | 2 Year Deal |
| Stephen Quinn | Burton Albion | Mansfield Town | 1 Year Deal |
| Callum Reilly | AFC Wimbledon | Leyton Orient | 1 Year Deal |
| Danny Rogers | Kilmarnock | Oldham Athletic | 1 Year Deal |
| Liam Scales | Shamrock Rovers | Glasgow Celtic | 4 Yr Deal €600,000 |
| Conor Shaughnessy | Rochdale | Burton Albion | 2 Year Deal |
| Cillian Sheridan | Wisla Plock-Poland | Dundee | 2 Year Deal |
| Ryan Sweeney | Mansfield Town | Dundee | |
| Ethon Varian | Stoke City | Raith Rovers | Loan to January |
| Stephen Ward | Ipswich Town | Walsall | 1 Year Deal |
| Corey Whelan | Wigan Athletic | Carlisle United | 2 Year Deal |
| Aidy White | Hearts | Rochdale | 2 Year Deal |
| Conor Wilkinson | Leyton Orient | Walsall | 2 Year Deal |
| Shaun Williams | Millwall | Portsmouth | 1 Year Deal |
| Tyreik Wright | Aston Villa | Salford City | Season Loan |
| Kevin Zefi | Shamrock Rovers | Inter Milan |