Son of former ACF Fiorentina goalkeeper Alessandro Mannini, Daniele started his professional career at hometown club Viareggio, playing with them in the Italian Serie C2 and Serie D tiers.
In summer 2003, he joined Pisa of Serie C1.
In 2004–05 season he joined Serie A club Brescia.[2] On 12 September 2004, he made his Serie A debut against Juventus. He stayed with Brescia after they were relegated to Serie B in summer 2005, and played with them until 31 January 2008.
He left for Serie A club Napoli on 31 January 2008, joining fellow Brescia players Santacroce and Hamsik, for a total fee of €18 million within a season. Mannini himself was tagged for €7 million.[3] In January 2009 he was handed a one-year suspension by the Court of Arbitration for Sport (CAS) along with former teammate Davide Possanzini from WADA for being late for a drugs test following a Serie B match between Brescia and Chievo in December 2007.[4] Later the ban was frozen by CAS due to appeal process.,[5] The ban was cancelled on 27 July 2009[6] after being proved there was no real intention to avoid the controls from Possanzini and Mannini.
In July 2009, Mannini joined Sampdoria in co-ownership bid, for €3.5 million (€7 million divided half).[7][8] On the same day Hugo Campagnaro joined Napoli for €7 million.
Mannini made an excellent start in his first season at Sampdoria, scoring 5 goals in Serie A and 3 assists in just 8 games.
At the end of 2010–11 Serie A, Doria was relegated. The club gave up the co-ownership and allowed players to return to their mother clubs for a peppercorn fee of €500 each, such as keeper Gianluca Curci and winger Stefano Guberti. However the co-ownership of Mannini was not resolved before the deadline on 24 June. Thus, both clubs had to submit a bid in a sealed envelope to Lega Serie A in order to decide the highest bidder, which was only €500.[9] on the other hand, Sampdoria abstain entirely from making an offer.[10]
On 6 August 2011, Mannini moved to newly promoted Serie A club Siena in another co-ownership deal for €450,000 (plus €200,000 other fee) in a 4-year contract.[11][12] In June 2013 Siena acquired Mannini outright for free[13] after the club was relegated. Both clubs failed to form any deal before the deadline, but Napoli did not submit a bid.[14]
On 31 January 2014 he was signed by the third-level club Pisa in a temporary deal.[15] He was released after Siena failed to register for 2014–15 Serie B.
On 1 September 2014 he was signed by US Lecce.[16]
Mannini was re-signed by Pisa on 27 August 2015.[17]
On 15 January 2020, his contract with Pontedera was terminated by mutual consent.[18]
Having been released by Pontedera, Mannini elected to retire from football, and moved to East Yorkshire to work as a sales executive for a food company.[19] During a chance encounter while they were both out walking dogs, Mannini met Mark Smith, the chairman of Beverley Town, a local team preparing for their first ever season in Division One of the Northern Counties East Football League, which saw Smith invite Mannini to pre-season training.[20] On 22 July 2022, Beverley Town announced that Mannini had joined them for the upcoming season.[21]
