In March 2012, Petrov was diagnosed with acute leukaemia, suspending his football career to undergo treatment which was ultimately successful.

At the age of 18 he was spotted by scout and coach Dimitar Penev and signed with CSKA Sofia for fee of €30,000.

[10] The following season, 2001–02, Petrov made his return from injury against Dunfermline Athletic in September,[11] and then really came into form for Celtic, being described as a dynamic, hardworking box-to-box midfielder,[7] and winning his second SPL medal.

Things started badly for Celtic as they lost 5–0 to Slovakian minnows Artmedia Bratislava in Strachan's first match.

Celtic overcame their bad start to the campaign to win the SPL and League Cup double.

He was subsequently linked with a transfer to move to Aston Villa who were managed by former Celtic boss Martin O'Neill.

Petrov scored his first Villa goal in a 2–2 draw against Sheffield United on 11 December 2006, but suffered patchy form throughout his first two seasons at the club.

[22] The 2008–09 season saw Petrov's form improve considerably as he became a first team regular, starting Villa's six Premier League games in a row.

On 26 December 2010, Petrov returned to first team action, coming on as a second-half substitute for Jonathan Hogg in the 2–1 defeat against Tottenham Hotspur at Villa Park.

On 29 October 2011, Petrov made his 200th appearance for Aston Villa in the Premier League clash with Sunderland, and scored the opening goal in a 2–2 draw.

[26] On 26 May 2013, footballers who had represented the Bulgaria national side (including Hristo Stoichkov, Dimitar Berbatov and Nasko Sirakov) won 4–2 against a selection that featured Aston Villa veterans like Mark Kinsella and Bryan Small in an exhibition game that took place at the Vasil Levski National Stadium in Sofia and had been organised to honour Petrov's achievements.

[27] In October 2014, Petrov began playing again for his local Sunday League Over-35s side Wychall Wanderers[28][29] who were managed by former Coventry City player David Busst.

[30] In April 2016 Petrov revealed he was training with Villa's Under-21 side with a view to returning to the professional game.

[33] Stilyan Petrov made his debut as a 52nd minute substitute[34] for Bulgaria on 24 December 1998 in a friendly match against Morocco.

In 2003, he won the Bulgarian Footballer of the Year award, when he was playing for Celtic and he captained the national team at Euro 2004 where he was sent off during a match against Denmark.

On 26 March 2011, Petrov earned his 100th cap for Bulgaria in the 0–0 home draw with Switzerland in a Euro 2012 qualifier.

He received a flower bouquet from Borislav Mihaylov and was applauded by the spectators prior to the start of the match.

"[42] He visited Villa Park for the match against Chelsea and in the 19th minute, the number of his shirt, the crowd gave him an ovation.

[48] Talking about his new role Petrov said ″I'm very excited by this new challenge and I wish to thank the Club and the manager, Paul Lambert, for giving me the opportunity to continue my association with Villa, which I have always regarded as a privilege.

[50] The Club announced his resignation and explained that he had requested time off as he felt he had to be fully devoted to his family.

[53] On 11 December 2014, Petrov appeared as a special guest on the eighth episode of the ninth series of Russell Howard's Good News.