His energy, leadership, creativity, skill and eye for goal from midfield saw him play a key role in helping the team to two Coppa Italia titles and a Supercoppa Italiana.

At international level, Hamšík helped Slovakia qualify for the country' first ever FIFA World Cup, captaining the side at the 2010 tournament as they reached the round of 16 following a victory over defending champions Italy.

[17] Three days later, Hamšík scored his second goal of the new season with an 81st-minute penalty to earn Napoli a 4–1 comeback win away to newly promoted Cesena.

[22] On 29 November, Napoli welcomed Serie A table leaders Juventus to the Stadio San Paolo;[23] Hamšík missed a 15th-minute penalty before heading in a goal to give the hosts the lead seven minutes later.

[24] The match was enthralling, however it ended in a 3–3 draw after Napoli conceded two late goals to preserve Juventus' unbeaten start to the season.

[33] The announcement was made following Hamšík scoring an incredible angled shot against Cagliari earlier that day, as Napoli ran out 6–3 winners.

[34] Hamšík's final goal of the season came in a 2–0 victory over Palermo on 1 May, as he doubled Napoli's lead in the 35th minute following a penalty from Edinson Cavani.

[39] Later that month, in Napoli's first league fixture of the 2012–13 Serie A season, Hamšík scored the club's first goal and assisted Christian Maggio's strike in an eventual 3–0 defeat of Palermo.

[40] Missing leading goal-scorer Edinson Cavani for the club's match against Chievo on 28 October 2012, Hamšík connected on a Juan Camilo Zúñiga cross to give Napoli a 1–0 victory.

[48] Following Paolo Cannavaro's departure to Sassuolo in the 2014 January transfer window, Hamšík was named Napoli's new captain.

[54] On 22 December, Hamšík lifted the 2014 Supercoppa Italiana as Napoli's captain, defeating Juventus 6–5 on penalties after a 2–2 draw following extra time.

[64] On 16 December 2017, Hamšík scored his 115th goal for Napoli in a 3–1 away victory over Torino, equalling Diego Maradona as the club's all-time top scorer.

[65] He surpassed Maradona's record one week later, becoming Napoli's outright all-time top goalscorer with his 116th goal for the club, which came in a 3–2 victory against Sampdoria in Naples.

[70] On 6 November, he overtook Bruscolotti with his 512th appearance in all competitions for Napoli in a 1–1 home draw against Paris Saint-Germain in the Champions League.

[72][73] On 3 March, in the opening match of the 2019 Chinese Super League season, Hamšík made his club debut in a 1–1 away draw against Henan Jianye.

[77] He made his debut for Göteborg on 19 April in a league game against AIK, replacing Simon Thern in the 73rd minute of a 2–0 win.

Hamšík captained his country in its first FIFA World Cup experience in South Africa in 2010, where the nation made it to the first knockout stage after defeating then-world champions Italy 3–2.

[90][91][92] At the final tournament, Slovakia suffered a closely contested 2–1 defeat to Wales in its opening match of the competition on 11 June.

Hamšík came close to opening the scoring in the third minute of play after dribbling past several Welsh defenders, but his strike was denied by Ben Davies' goal-line clearance.

[92] In Slovakia's second group B match of the tournament, against Russia on 15 June 2016, Hamšík had set up a goal for Vladimír Weiss and later scored another himself in a 2–1 win, his nation's first in the competition.

[95] On 5 October 2017, Hamšík made his 100th appearance for the Slovak national team in a 0–1 loss to Scotland in a 2018 FIFA World Cup qualification match.

[102] Earlier in the month, on 17 November, the national team also featured in another friendly at Podgorica City Stadium versus Montenegro.

[104] For his retirement match versus Chile, on 17 November, Hamšík expressed that he hoped to fill up the Tehelné pole stadium.

[109] In play, Hamšík continued to be a key player of Slovakia completing about 90 passes, with almost 90% accuracy with the media noting his cooperation with László Bénes.

[111] During the post-match press conferences and media appearances, Hamšík did not rule out the option to re-join the national team in a managerial or coaching positions in the future.

[112] In June 2023, Hamšík was recalled as an emergency call-up to the national side for their UEFA Euro 2024 qualifying matches due to numerous injuries in the midfield.

Hamšík has been described as "quick, energetic, hard-working, and tactically versatile midfielder, who was capable of playing in several offensive positions on either side of the pitch, or even through the centre".

Hamšík refused the further undisclosed offer in order to concentrate on national team, private footballing academy and family commitments.

[132][133] In 2015, Hamšík represented Slovakia and co-starred in events at the country's pavilion at Expo 2015 in Milan along with Slovak President Andrej Kiska.

[138] His brother-in-law Walter Gargano has made him an avid fan of the Uruguayan team Club Atletico Peñarol, having been seen at matches before.