Bothroyd will be reunited with manager Dave Jones, who signed the 30-year-old for Cardiff in August 2008.
He scored 45 goals in 128 appearances for the Bluebirds in the Championship, earning him a surprise inclusion in Fabio Capello's England squad for the 2-1 friendly defeat to France in 2010.
Sheffield Wednesday have also secured the signing of Watford defender Martin Taylor for an undisclosed fee.
The experienced 32-year-old has penned a two-year deal at Hillsborough.
Taylor joined Watford on a free transfer in January 2010 and made 95 appearances for the club, scoring 10 goals.
Swindon have signed Wednesday midfielder Giles Coke on loan until January.
Cardiff have secured the signing of West Ham striker Nicky Maynard.
The 25-year-old has penned a three-year deal at the Cardiff City Stadium and will be able to make his debut in Sunday's home npower Championship clash with Wolves.
Nottingham Forest have bolstered their squad with the loan deadline-day signings of striker Billy Sharp and midfielder James Coppinger.
Sharp, 26, will spend the rest of the season on loan from Premier League newcomers Southampton while Coppinger, 31, has joined from Doncaster until January 2.
The pair are reunited with Forest boss Sean O'Driscoll, who managed them at Doncaster, and are available to make their debuts in Saturday's npower Championship clash with Charlton at the City Ground.
Chairman Omar Al Hasawi told the club's official website: "No manager knows Billy as well as Sean does and when he made it clear he wanted to bring him to the club we did everything in our power to make it happen.
"Billy's goalscoring record is outstanding and we have no doubts he will fit in perfectly at the City Ground and add to the attacking threat we already have.
"James has great experience of the Championship and I know he is delighted to have the opportunity to work with Sean again. He is our 11th signing for Nottingham Forest and I'm sure he will prove to be a great asset for us in the weeks ahead."
Forest striker David McGoldrick has joined midlands rivals Coventry on loan.
Blackburn have completed the double capture of Diogo Rosado and Nuno Henrique on three-year deals, subject to international clearance.
Attacking midfielder Rosado, 22, joins from Sporting Lisbon while central defender Henrique has left fellow Portuguese side Academica De Coimbra, with both men committing to Rovers until 2015.
They arrive at Ewood Park along Grzegorz Sandomierski, who earlier joined on a season-long loan from KRC Genk, and take Steve Kean's summer recruitment drive to 12 players.
Brighton secured their third deadline-day signing by bringing Athletic Bilbao midfielder David Lopez to the Amex Stadium.
The 29-year-old Spaniard has penned a one-year deal after passing a medical and joins Andrea Orlandi and Scott Dobbie in moving to the south-coast club.
While Dean Hammond has rejoined hometown club Brighton on a one-year loan from Southampton.
Boss Guy Poyet finally captured 29-year-old Dobbie, who will link up with his new team-mates on Monday, having been chasing his signature all summer.
Poyet said: "He is a quality striker, who will complement our existing forwards and give us different attacking options.
"He has great quality which will unlock defences and I have no doubt he will also score plenty of goals.
"He has played and proven himself at this level and in the Premier League. His goals helped Blackpool win promotion in 2010 and he returned on loan to help them reach the play-off final last season."
Hull have completed the signing of Sheffield United midfielder Stephen Quinn for an undisclosed fee.
Quinn has signed a three-year deal with the Tigers, ending a seven-year association with the Blades.
He progressed through the youth system at Bramall Lane before making his debut against Shrewsbury in 2005.
The 26-year-old was named in last season's PFA League One Team of the Year and also topped the assist charts.
Hull winger Cameron Stewart has joined Championship rivals Burnley on a loan deal until January.
The 22-year-old joined the Tigers from Manchester United in January 2011 following a successful loan spell.
Stewart has made 50 appearances for City, three this season, but with competition for midfield places fierce after the signings of Ahmed Elmohamady and Stephen Quinn, manager Steve Bruce has allowed Stewart to leave.
The deal was completed in time for the winger to play in the Clarets' home match against Brighton on Saturday.
Birmingham have completed the loan capture of Swindon right-back Paul Caddis on a season-long deal, with striker Adam Rooney heading in the opposite direction on the same terms.
Caddis skippered the Robins to the League Two title last year but has not featured at all this term after falling out of favour with manager Paolo Di Canio.
He was stripped of the Swindon captaincy just over two weeks ago after Di Canio questioned a change in attitude from the 24-year-old.
The former Celtic defender, who only penned a new contract with the League One club earlier this summer, could now make his debut for Blues in Saturday's home clash against Peterborough.
Peterborough have signed highly-rated midfielder Kane Ferdinand from Southend.
Ferdinand, cousin of Manchester United defender Rio and QPR's Anton, has moved to London Road on a four-year contract for a fee that could net the Shrimpers over £500,000.
The teenager will not be involved in Saturday's npower Championship fixture at Birmingham as the transfer was completed after the noon deadline.
Posh also had a bid rejected by Southend for winger Ryan Hall earlier in the day.
Bolton have completed the signing of Liverpool midfielder Jay Spearing on a season-long loan.
The 23-year-old joins the club with exceptional pedigree having already made over 50 appearances for the Premier League side.
"We have been in the market for a player of this kind for a long time and Jay is someone that we have always had an eye on," manager Owen Coyle told the club's official website.
"He was previously never available and, indeed, played the majority of games in Liverpool's first team last season in the Premier League.
"We did everything we could to bring Jay to the football club and so we are thrilled to bring in a player of his calibre.
"He is a young player that is driven, who is a terrific passer of the ball. He has a real desire to do well and has all the attributes that we crave at Bolton Wanderers."
Carlisle have completed the signing of Bolton forward Michael O'Halloran on a one-month loan deal.
The 21-year-old goes straight into the squad for Saturday's game against MK Dons.
O'Halloran came through Wanderers' youth system and enjoyed a loan spell with Sheffield United last season.
The Scottish-born striker has represented his country at Under-17, Under-19 and Under-21 level.
Watford manager Gianfranco Zola has moved to sign five players on loan from Udinese on deadline day with an option to sign them on a permanent basis.
Defenders Jean-Alain Fanchone, Neuton Piccoli and Lars Ekstrand as well as midfielder Cristian Battocchio and striker Fernando Forestieri have joined the npower Championship club.
The transfers are subject to international clearance.
Zola has also raided former club Chelsea to sign versatile youngster Nathaniel Chalobah on loan until January.
The defender-come-midfielder, 17, captained the Blues to FA Youth Cup success last term and has also skippered the Premier League club's reserve side on a regular basis.
Chalobah, an England Under-19 international, is yet to make a first-team appearance for Chelsea but has been an unused substitute.
Crystal Palace have signed Blackburn striker David Goodwillie on loan until January.
The 23-year-old has fallen out of the picture after heavy recruitment from Rovers this summer, with four strikers arriving at Ewood Park.
The move will be a relief to Palace manager Dougie Freedman, who earlier missed out on Jay Bothroyd after the QPR striker joined Sheffield Wednesday on loan.
They have completed the deadline-day signing of defender Damien Delaney on a free transfer.
Huddersfield have signed Wolves winger Adam Hammill on loan.
The 24-year-old, who arrived at Molineux in 2011, will stay at the John Smith's Stadium until January.
He will be unable to play when the two sides meet in the npower Championship later this year.
Ryan Stevenson has parted ways with Ipswich by mutual consent and rejoined former club Hearts on a three-year deal.
Leicester defender Cian Bolger has joined Bristol Rovers on loan for a third time. The 20-year-old Irishman, a graduate of the Leicester Academy, had previous spells at the Memorial Stadium in 2011 before spending the whole of last season with the Pirates.
Defender Damion Stewart has left Bristol City after his contract was terminated by mutual consent. The 32-year-old made 24 appearances for the Robins having signed from QPR in 2010 and is now free to join another club. Manager Derek McInnes said: "I'd like to thank Damion for his time at the club and wish him all the best for the future."