After spending two years in the youth team, during the 2005 season Berg was promoted to the regular squad and played for IFK Göteborg in the Allsvenskan.

[2] Berg played for IFK Göteborg until the 2007 summer and put forth an attracting performance throughout his final season, as he maintained a high scoring efficiency throughout the league matches.

[3] On 10 August 2007, Dutch club FC Groningen signed Berg for a reported £2.5 million[4] to replace the departing Ajax-bound Luis Suárez.

On 17 July 2009, German Bundesliga side Hamburger SV confirmed that Berg had signed a five-year contract with the club.

Dagblad van het Noorden, a Dutch newspaper, stated that Berg swapped clubs for €10.5 million.

Although initially the fee of €9.5 million was too high for Hamburg, Berg's desire of moving to the Bundesliga persuaded Groningen to complete the transfer.

[8] After returning from his loan spell at PSV, Berg only made 13 appearances the 2011–12 Bundesliga due to injuries and continued lack of form, scoring once.

[16] Additionally, Marseille tried to complete a move for the Swedish striker on the deadline date, however, they were put off by Panathinaikos's price tag.

But it's pretty clear that I want to play as I'm in a decent form," the Panathinaikos striker underlined straight after the game.

[20] On 6 March 2016, Swedish striker and fans of Panathinaikos' favorite Berg reached 100 official appearances with the Greek club at a home game against Atromitos.

[24] On 18 August 2016, Berg was the scorer of two goals, helping Panathinaikos win the first leg of the UEFA Europa League play offs and is set to qualify for the group stage, as the Greens crushed Danish Brøndby IF 3–0 at Leoforos stadium.

[25] On 6 September 2016, Berg stepped into retired Sweden national team captain Zlatan Ibrahimović's vacant boots to open the scoring in Stockholm just two minutes before the break against Netherlands, as he capitalised on Kevin Strootman's defensive mishap to smash in from outside the box into the top left corner.

[35] On 30 April 2017, he scored his last goal for the season, in a 2–0 home win against AEL gaining the title of the 2016–17 League top scorer for first time in his Greek career.

The 31-year-old international and captain of the Greens showed unprofessional behavior on home clash against PAOK (1–0), which was finally interrupted by referee Giorgos Kominis at 55', and will not perform at the four remaining matches.

[36] On 20 June 2017, the Administration of Panathinaikos rejected the first offer of Al Ain FC (€2.5–3 million) about the purchase of experienced Swedish striker.

The Greens are holding the 55% of the rights of 31-year-old international (his former team, Hamburger SV, have the other 35%), whose current contract expires in the summer of 2019, with a buy-out clause of €5.2 million, but the negotiations with the UAE club are expected to be continued, while Berg has already agreed to sign a two (plus one) years' season contract with Al Ain, with an annual salary of €3 million after taxes.

[37] On 28 June 2017, however, Al Ain FC confirmed the move was finalised following lengthy negotiations with Panathinaikos, with the figure believed to be around €3 million.

"[38][39] On 16 April 2018, following an incredible season in UAE Pro-League, Berg was twice on target as his club advanced to the last 16 stage of the AFC Champions League with an emphatic 4–1 rout of Qatar's Al Rayyan SC.

[49] Berg featured in both matches of the Champions League play-off tied against PAOK in September 2020 as Krasnodar won 4–2 on aggregate to secure qualification to the group stage for the first time in club history.

[61] He was on the score sheet also in the final match day against Albania, netting the second in an eventual 4–1 home win, which was not enough to secure Sweden a place at the tournament.

At 2014 FIFA World Cup qualification, Berg was part of the team only in the first Group C matches; he made only two appearances, both as replacement, netting only one time in the 2–0 home win over Kazakhstan on 11 September 2012.

[67][68] At play-off round, Berg made two appearances as Sweden eliminated the rivals of Denmark 4–3 on aggregate to secure a spot at UEFA European Championship for the 5th consecutive edition.

[71] Berg also appeared in the remaining matches as Sweden lost to both Italy and Belgium which brought the elimination from the tournament.

[72] Berg was Sweden's main striker during the 2018 FIFA World Cup qualification after the retirement of Zlatan Ibrahimović.

[74] On 7 October 2017, Berg scored four goals as Sweden ran riot in front of a record crowd of 50,022 at the Friends Arena, hammering Luxembourg 8–0, in their biggest win in 79 years, to make a great step to the 2018 FIFA World Cup finals.

[82] On 15 October 2019, Berg scored his 20th senior international goal for Sweden in a 1–1 draw in a UEFA Euro 2020 qualifying game against Spain.

[83] On 8 September 2020 in a 2020–21 UEFA Nations League game against Portugal, Berg served as Sweden's team captain for the first time.

[85] Following Sweden's opening game in Euro 2020 against Spain in Seville, Berg became the target of severe online abuse and hatred after missing a chance to score.