On 10 August 2005, just before she turned 21, Melua became a British citizen along with her parents and brother. The citizenship ceremony took place in Weybridge, Surrey. Becoming a British citizen meant that Melua had held three citizenships before she was 21; first Soviet, then Georgian and finally, British.
Melua's second album, Piece by Piece, was released on 26 September 2005. Its lead single was the Mike Batt song, "Nine Million Bicycles", which was released a week before the album on 19 September and was number three in the UK singles chart. The album contains four more songs written by Melua herself, four more by Batt (including "Nine Million Bicycles"), one Batt/Melua collaboration and three more songs described as new versions of "great songs". The band line-up was the same as on the first album. The album debuted at the number one spot on the UK Albums Chart in the week of 3 October 2005. This album broke Melua across Europe where it sold 1 million copies in Germany alone and achieved the number one position in Billboard's "European" albums chart. It was 4X platinum in UK and in Ireland, 3X platinum in Norway, Denmark, Holland and Germany, 2X platinum in Poland and Switzerland and at least platinum or gold in France, Iceland, South Africa, Austria, Belgium, New Zealand and Sweden. Worldwide sales to date are in excess of 3.5 million.
On 30 September 2005, Melua came under criticism in The Guardian from writer and scientist Simon Singh for the lyrics (written by Mike Batt) of the track "Nine Million Bicycles". Batt's disputed lyrics were:
Melua has stated that the rock band Queen were a huge influence on her as a child/teenager, with one of her memories of music being her uncle playing records by Queen and Led Zeppelin. She performed with Queen at the 46664 concert in South Africa in March 2005.