Marklund's Grammis Award-winning[1] third studio album In Orbit was released in 2005 and spawned two hit singles; "Satellites" and "Cry for You," which made it to No.

"Cry for You" remains the most successful international single of her career and was also nominated for the Government's Music Export Prize 2008 in Sweden for selling more than a million copies worldwide.

In Sweden, Marklund had her biggest success with the Swedish-language single "Mikrofonkåt", originally performed by Swedish rapper Petter.

It became her first number-one hit in her native country, held the top position for 11 consecutive weeks,[2] and was certified 8× Platinum.

[7] Marklund began recording music in studios at age 12, but did not commercially release material until later.

[13] After a silence for a while, September later signed to her current label CatchyTunes, and later released the single "Satellites" on 6 July 2005.

[14][15] The song currently stands at number 139 in the Swedish All-time best performing in the Singles Chart being certified as Platinum.

[18] The song was certified Gold by International Federation of the Phonographic Industry (IFPI) in Sweden.

She became the first Swedish singer to receive a certification in the United States since Ace of Base's 1998 hit, Cruel Summer.

[22] The song was also successful in the Oceanic regions, as it peaked at fourteen in Australia and thirty-nine in New Zealand.

September released a new single entitled "Can't Get Over" on 20 June 2007 in Sweden and peaked at number five on the charts.

On 26 February 2008, Marklund released her debut album in the US, Canada and Australia called September.

"Can't Get Over" was released in the United Kingdom, and peaked at fourteen on the UK Singles Chart.

[29] September released her fourth studio album Love CPR on 11 February 2011 in Sweden.

[33] The song peaked at thirty-two on the Swedish Singles Chart, and released a music video, along with "Me & My Microphone".

[38][non-primary source needed] She hosted weekly sing-along show Allsång på Skansen on SVT during 2014–15.

[39] A media critic commented: "The previous two years with Petra Marklund does not go down in history as a success.

Not that she was an exceptionally bad host, but it felt like every Tuesday there were about seventy eleven places she would rather be than on the Solliden stage.

"[40] Marklund released her second Swedish-language studio album Ensam inte stark on 13 November 2015 under her true name, not her previous stage name, September.

[43] Ensam inte stark has been described as dark and deep electronica album with themes of sadness, loneliness, disappointment and heartbreak.

[44][45] In early 2016, touring under her own name, ticket sales were poor in Umeå and Luleå, both in the north of Sweden, and she was forced to cancel several concerts.

Subsequently, on 27 October 2023, she unveiled an acoustic rendition of the song, distributing it through her independent record label, Petra Marklund Productions AB.

In the earlier period, she stated in an interview that after the release of Teen Queen, "People think I am stupid just because I have blond hair and sing dance music.

"[6] In "The Story of September", she said that her biggest influence and idols were Kylie Minogue, Sophie Ellis-Bextor, Lily Allen, Kanye West and Madonna.

Lyrically, her songs of the early era tended to stay in the vein of love or heartbreak.

Most of the songs are original arrangements; however "Midnight Heartache" from the In Orbit album contains a sample of "Bette Davis Eyes" by Kim Carnes.

"[47] In 2011, her image had changed which includes avant-garde fashion and her platinum-blonde hair, which was styled in a boy cut for her "Resuscitate Me" video.

"[47] Petra Marklund provided the vocals for a song by German electronica project Schiller.

[50] On 16 November 2010, September released a cover of Petter's Mikrofonkåt after she performed it on Så mycket bättre.

[51] On 24 December, September released a duet with Petter from Så mycket bättre and it peaked at number 3 on the Swedish chart.