Icardi was born in Rosario, Argentina and moved to Canary Islands when he was nine. He began his football career with Vecindario in Gran Canaria, and scored over 50 goals in their youth categories.

In 2007, he was disputed over by Barcelona and Real Madrid, after offers from Valencia, Sevilla, Espanyol, Deportivo La Coruña, Arsenal and Liverpool. Barcelona won the race for Icardi, and signed with him until 2013.

Icardi joined the Catalan club at the start of 2008–09 season and was included on the U-17 team. He was promoted to the U-19 team the following season before joining Sampdoria on loan in January 2011. Icardi later stated that leaving Barcelona was not a bad decision, convinced that his decision to move on was the right one.

On 11 January 2011, Sampdoria confirmed Icardi had signed with the club on loan until the end of the season. After a successful six-month loan for la Samp, scoring 13 goals in 19 games with the Primavera team, the Italian side utilised the option to buy Icardi for €400,000 in July 2011, signing a three-year deal. In 2011–12 season, he scored 19 goals in the reserve league Group A, as the joint-third topscorer of the league along with Gonzalo Barreto of Group C.

On 12 May 2012, he made his first-team debut, against Juve Stabia, after coming off the bench to replace Bruno Fornaroli in the 75th minute of the match. Ten minutes later, Icardi scored his first professional goal to win the match 2–1 for Sampdoria.

On 26 September 2012, he made his Serie A debut for Sampdoria against Roma, substituting the Paraguayan midfielder Marcelo Estigarribia in the 49th minute. On 12 November, Icardi scored his first goal in Serie A in the Derby della Lanterna against Genoa in an eventual 3–1 win. On 6 January 2013, he scored two goals against Juventus in Sampdoria's 2–1 upset at Juventus Stadium. It was Juventus's second ever loss in the Juventus Stadium since the construction.

On 27 January 2013, he scored four goals in a six-goal thrashing of fellow strugglers Pescara, lifting the Genoese side clear of the Serie A relegation zone. On 18 May, during the final match of 2012–13 season, Icardi scored again against Juventus, helping the team to beat the eventual champions of Italy 3–2 at Stadio Luigi Ferraris.

In late April, it was announced that Icardi would join Inter Milan before the beginning of the 2013–14 season. The deal was also later confirmed by Sampdoria board. The transfer fee was €6.5 million for 50% registration rights. Icardi was officially unveiled as an Inter player on 16 July along with Algerian striker Ishak Belfodil, where he was allocated squad number 9. He said that moving to Inter is a "dream come true", adding that he "had a lot of offers, but wanted only Inter".

He made his unofficial debut one day later during the 3–0 away win against Trentino Select XI by playing in the first half of the 3–0 away win. He scored his first goal for Inter in their 1–1 pre-season friendly draw with Bundesliga club Hamburger SV, netting after less than two minutes on the field and being assisted by Fredy Guarín.

On 25 August 2013, Icardi made his Inter official debut, coming on as a second-half substitute in a 2–0 home success over Genoa, hitting the crossbar late in the game; he scored his first league goal for the Nerazzurri on 14 September, netting the first of a 1–1 home draw against Juventus, after coming on as a substitute in the 73rd minute.

Due to injury, Icardi missed most of the games of the first part of the season, only returning to first-team matches in February. On 14 February 2014, during the away match against Fiorentina at Stadio Artemio Franchi, Icardi returned in the field after four months and scored the winner after only ten minutes. Later, on 5 April, Icardi scored a brace during the 2–2 home draw against Bologna. That was his first brace of his Inter career. This was followed by another brace during the 0–4 away win against his former side Sampdoria. Before the match, he was booed by the home fans, but he quieted them down by scoring in the 13th minute from a cross from Palacio, making a negative gesture which saw him booked.

On 10 May 2014, in Javier Zanetti's last competitive match at the San Siro, in which Inter defeated Lazio 4–1 to secure a place in Europa League play-off for next season, Icardi scored the second goal of the match in the 37th minute after an assist from Kovačić and went to celebrate with Zanetti. He ended his first season with Nerazzurri with 23 matches in all competitions, including 22 in the league, scoring 9 goals in the process with an average of one goal in every 145 minutes.

On 10 June 2014, Inter and Sampdoria reached the deal to terminate the co-ownership for another €6.5 million, making Inter was the sole employer of Icardi in the football field.

Icardi playing for Inter Milan in 2014
Icardi playing for Inter Milan in 2014
On 20 August 2014, in Inter's first match of the season against Iceland's Stjarnan for first leg of play-off round of the 2014–15 Europa League, Icardi opened a 3–0 away win. That was his first European goal, in his European debut. In the returning leg, he came in as a second-half substitute and scored two times in a 6–0 win at the San Siro, to advance his team into the group stage 9–0 on aggregate.[citation needed]

During the second match of the league season on 14 September, he scored his second Serie A hat-trick in a 7–0 thrashing of Sassuolo. Ten days later, Icardi was injured and substituted in the 24th minute for Dani Osvaldo during the 2–0 home win against Atalanta. On 26 October, Icardi netted his first Serie A goal for over a month, the winner on a penalty kick against Cesena and giving Inter their first away win of the league. He was decisive again three days later, scoring a 90th-minute penalty kick won by Zdravko Kuzmanović in a 1–0 win against Sampdoria, giving his former side their first loss of 2014–15 season.

On 9 November, Icardi scored twice after two assists by Palacio during a 2–2 home draw against Hellas Verona. This draw caused the sacking of coach Walter Mazzarri, who was replaced with the returning Roberto Mancini. On 6 January of the following year, in the first match of the second part of the season, Icardi netted the only goal for his team during the 1–1 draw against Juventus at Juventus Stadium; the goal came in 64th minute after a pass from the Colombian midfielder Fredy Guarín. During that match, he had a conflict with his strike partner Osvaldo who was angry with him after Icardi decided to shoot instead of passing to his teammate who was in a better position to score. Due to this, Osvaldo left the team in the end of January.[citation needed] Five days later, Icardi was decisive in Inter's 3–1 home win against Genoa, scoring the second goal and earlier making an overhead kick (saved by goalkeeper) which was turned into an assist for Palacio.

In the match against Sassuolo, Inter lost 1–3 with Icardi scoring the only goal for his team after a mistake from the Sassuolo defence. After the match, he along with Guarín had a conflict with the fans at the Mapei Stadium. They went to throw their shirt to the fans who refused and threw them back at them, spewing insults at them. On 7 February, Icardi responded by scoring twice in a 3–0 home win against Palermo, refusing to celebrate in the process. After the match Icardi told to the media that the reason he did not celebrate was not the conflict with the fans but failing to find a way to renew his contract with the club directors. He was later criticized by Mancini for not celebrating.

On 11 April, he scored the first goal during the 0–3 away win against Verona, helping Inter get their first win after six consecutive matches. He scored twice on the final day in a 4–3 win over Empoli and finished the season as the joint Serie A top goalscorer with 22 goals with Verona'