[1] He worked nine years as primary school teacher,[2] and played amateur football during his freetime for local teams such as Deruta, Cannara, Spello and Pontevecchio,[3] in the role of midfielder.

In 2000, Cosmi received the highest possible mark in the Coverciano coaching course;[5] his thesis was entitled "Il Trequartista" ("the advanced playmaker," in Italian football jargon).

He guided the team for four consecutive years, winning a UEFA Intertoto Cup, showing valid coaching abilities and launching several players, including 2006 FIFA World Cup winner Marco Materazzi (who reached a career high of 12 goals in a single season under Cosmi's tenure), then-unknown Japanese Hidetoshi Nakata, Fabrizio Miccoli, Fabio Grosso and Fabio Liverani.

After his short, but successful, experience with Genoa, Cosmi was signed as new coach of Udinese, in order to replace Luciano Spalletti, who gained the qualification to the preliminary rounds of Champions' League the previous season.

But it was Cosmi who led the team on the European competition, defeating Sporting Clube de Portugal in a two-tier qualifying round.

Despite fairly good results at the helm of Livorno, Cosmi resigned from his coaching post on 24 January 2010, in the wake of a 2–0 home loss to fourth-placed Napoli due to disagreements with club chairman Aldo Spinelli.

Following the meeting, both parties agreed that the head coach's resignation offer would have been rejected and Cosmi would return at Livorno with immediate effect.

[10] After more than a year without a job, Cosmi returned into management on 28 February 2011, taking over coaching duties at Palermo as a replacement for Delio Rossi, who was dismissed from the Sicilian club following a record 0–7 home defeat to Udinese.

[11][12] At Palermo, Cosmi reunited with former players Fabrizio Miccoli and Fabio Liverani, as well as ex-player and team staff member Giovanni Tedesco.

[15] On 24 February 2014, Cosmi returned into management as new head coach of Serie B club Pescara, replacing Pasquale Marino[16] but failing to turn the team fortunes and missing out qualification for the promotion playoffs.

[23] After failing to save his team from relegation to Serie B, with Crotone ending in 19th place in the league, the club announced they would not confirm Cosmi for the following season.