Rossi was born in Rimini. His playing career was not a bright one, as he reached his personal top from 1981 to 1983, playing Serie B with U.S. Foggia, where he spent most of his footballing time. He retired in 1989, after a season played with Fidelis Andria of Serie C2.
Rossi, a sports science graduate with honours, took his first coaching job in 1990, aged 29, at Torremaggiore, of Promozione league, immediately winning the championship. The next year he joined Foggia as youth coach. In 1993, Rossi signed for Salernitana of Serie C1, and led the team to a Serie B promotion. After an unlucky comeback to Foggia, and a sixth place in Pescara, Rossi returned to coach Salernitana in 1997, leading the team to its second Serie A promotion in history. Rossi guided the team in Serie A too, but was fired in March 1999, as he was unable to lead Salernitana out of the relegation positions.
A troubled year in Genoa and a poor comeback to Pescara were followed by three seasons with Lecce. Rossi, appointed as Lecce's coach in February 2002, was not able to avoid relegation to Serie B, but led the team back to Serie A just the next season, and maintained a place in the division the next year. He left Lecce in 2004 to be replaced by his maestro Zdenek Zeman, who was head coach at Foggia during Rossi's times in leading its youth team.
In December 2004, Rossi replaced Andrea Mandorlini at the helm of Atalanta B.C., last-placed in Serie A. Despite all his efforts and numerous praises, Rossi was not able to let his team escape from relegation. He is right footed.
Despite not saving Atalanta, his good efforts at the helm of the Dea club gained interest from Lazio, who appointed him as replacement for Giuseppe Papadopulo.
His time at Lazio has been a remarkable success for which he has aroused interest from many top Serie A clubs. Rossi guided Lazio to a surprising UEFA Cup place in the 2005–2006 season, only for the place to be lost as part of the Calciopoli scandal that rocked the country in the summer of 2006. Even more remarkable, however, was Rossi's feat the following season. Despite an initial 11-point points deduction (which was subsequently reduced to 3 on appeal), Rossi guided the biancocelesti to an unlikely third place Serie A finish and a place in the 2007–08 UEFA Champions League. However, during the 2007–08 season, he led Lazio to a disappointing 12th-place finish.
On 13 May 2009 Rossi led Lazio to their first trophy since the Coppa Italia triumph in 2004. It was also a Coppa Italia victory, which came after a successful penalty shootout against Sampdoria. On 8 June 2009, Delio Rossi was announced to have left Lazio because of personal reasons allegedly linked to an unstable working relationship with chairman Claudio Lotito. He was replaced by Davide Ballardini.
On 23 November 2009 Rossi returned into management as new head coach of Palermo, replacing Walter Zenga at the helm of the rosanero. He immediately managed to turn the fortunes of Palermo, guiding the Sicilians to quickly rise up the Serie A league table also thanks to surprise results such as two 2–0 away win against teams such as AC Milan and Juventus, and ending the season in fifth place with only one point behind fourth-placed Sampdoria who were admitted to the UEFA Champions League third qualifying round at the rosanero's expense. He was consequently confirmed as head coach of Palermo for the 2010–11 season, during which he also guided the club in its 2010–11 UEFA Europa League campaign. Impressive results in the new season included another impressive win at Juventus' home, as well as his abilities in launching youngsters as Javier Pastore, Ezequiel Munoz, Josip Ilicic and Armin Bacinovic.
Rossi was sacked on 28 February 2011 by club president Maurizio Zamparini following a record 0–7 home loss to Udinese; he was replaced by Serse Cosmi. However, Rossi returned at Palermo only four weeks later, after Cosmi's Palermo side was soundly defeated by Catania in the Sicilian derby later on 3 April. Following a surprising comeback, he led the club to the Coppa Italia final which the 3–1 defeat by Internazionale. During the pre-season, on 1 June 2011, Rossi resigned as Palermo manager by mutual consent with president Zamparini.
On 7 November 2011, Rossi returned into management as new head coach of Serie A club Fiorentina, replacing Sinisa Mihajlovic, dismissed because of poor results. Rossi's debut match as Fiorentina boss ended in a 0–0 home draw against incumbent champions Milan. Afterwards, Fiorentina lost 2–0 to Delio's former club Palermo. He later beat Empoli 2–1 in the Coppa Italia. In the following weeks, he put Fiorentina up to 10th place in Seria A after they beat Roma 3–0. The following games however saw Fiorentina dropping into the table down to 17th place at some point, and thus involved in the fight to escape relegation.
Rossi's time with Fiorentina ended in shocking fashion. On 2 May 2012, during a home game against 19th-placed Novara, Rossi decided to substitute Serbian striker Adem Ljajic in the 32nd minute with Fiorentina losing 0–2. The player ironically applauded the substitution as he left the pitch and further gave the coach ironic thumbs up from the dugout, to which Rossi reacted by physically assaulting Ljajic, pushing the youngster from above, then jumping after him into the dugout while attempting to punch him. After the game (ended in a 2–2 draw), the club board announced to have immediately removed Rossi from his position due to his actions, with two games still to go in the league season. The incident also cost him a three-month ban from Italian football, effective from 3 May 2012.
Rossi was appointed head coach of Sampdoria in December 2012 to replace Ciro Ferrara, becoming the seventh coach to work with both Genoa and Sampdoria. During his coaching tenure with the club, Rossi helped the Blucerchiati avoid relegation at the end of the 2012–13 Serie A season. On 11 November 2013, Rossi was sacked from his post, with Sampdoria in 18th position in the Serie A table having earned just 9 points and won only twice in 12 Serie A matches during the 2013–14 Serie A season. Sampdoria had lost its last three Serie A matches, including a 2-1 defeat at Fiorentina on the day of Rossi's dismissal. Rossi hinted after the Fiorentina defeat that ‘trust’ between himself and the club was becoming an issue. “If there is a time where you do not feel that the trust is there, you should not wait to see how things unfold. I am a man of the world and I think that if the confidence is there, then it is normal that one continues, but if it is not, then it is better to end the rapport regardless of the results,” he said.
On 4 May 2015, Rossi was named the new manager of Bologna in Serie B replacing Diego Lopez He was sacked by Bologna on 28 October 2015.
Winners : 2008–09
Runners-up : 2010–11