Mika worked with producer Greg Wells, who also produced his debut album Life in Cartoon Motion. The album was written in Olympic Studios, London, which began in June 2008. In September 2008 he moved to Rocket Carousel Studios, Los Angeles, where the album was recorded. Mika has described the album's themes as dealing with his teenage years, and "in a sense is kind of part two" of his first album. In contrast to his first album, which "contained innocent fairytales", Mika pitches the new album's songs as "gothic Tim Burton-esque fantasies."
The album was originally titled We Are Golden after the first single from the album, "We Are Golden". On 20 July 2009 in an on-air interview with DJJo Whiley on BBC Radio 1, Mika revealed he was considering renaming the album, because he wanted "something a little more ridiculous." On 6 August 2009 it was confirmed that the album's title would change to The Boy Who Knew Too Much. As with Mika's debut album Life in Cartoon Motion, the album artwork has been designed by Mika's sister (who works under the nom de plume DaWack), the Australian illustrator Sophie Blackall, Airside collaborator Richard Hogg and Mika himself. The artwork has been inspired by children's picture books from the 1940s to 1970s.
"We Are Golden" was the first single from the album. It received its UK radio debut on BBC Radio 2 on 20 July 2009. It peaked at #4 in the UK Singles Chart.
"Rain" was the second UK and German single, released on 23 November 2009 in both digital and physical format. It peaked at #72 in the UK Singles Chart, making it Mika's first UK single to miss the Top 40. In Germany it peaked at #56. It was released as the third UK single, on 15 February 2010.
"Blame It on the Girls" was the second American and Japanese single from the album. It peaked at #1 in Japan but failed to make any impact in the United States. It was released as the third UK single, on 15 February 2010. It peaked at #72.
The song "Good Gone Girl" charted within the Romanian Top 100 on airplay only, without being released as a single.
The album debuted at #4 on the UK Albums Chart and remained on the Top 40 for four weeks. The album debuted at #1 on the French Albums Chart, becoming Mika's second consecutive album to reach the top of the French albums chart and the album is double platinum with more of 200,000 copies sold. In the USA, the album debuted at #19 on the Billboard 200. In Italy the album debuted at #10 on the Italian Albums Chart, and it has been certified Gold with more of 50,000 copies sold.