Talented Mihaylov started as a youngster with home country top team Levski Sofia, making his full 90 minutes debut at the age of just 17 in the UEFA cup match against Auxerre.

Mihaylov's poor performances in some matches, particularly his blunder in the Champions League game against Werder Bremen on 31 October 2006, provoked a negative campaign among Levski supporters who associated his career with protection from his influential father.

On 29 July 2009, Mihaylov came on as a substitute for midfielder Kenneth Perez, following the dismissal of starting keeper Sander Boschker in the 27th minute of Twente's away game against Sporting CP in the first leg of the UEFA Champions League third qualifying round.

In the Champions League FC Twente drew to play against his "nightmare" club Werder Bremen, as it were mentioned by the Bulgarian media.

Mihaylov was quoted saying that Liverpool now had retained an option to buy him back from Twente, as he had played enough games for his native country's national team to qualify for a work permit.

On 23 December 2011, Mihaylov attended a ceremony in Sofia, where he was honoured with the Bulgarian Footballer of the Year award (Stiliyan Petrov and Dimitar Berbatov came second and third respectively).

[12] On 26 November 2018, Mihaylov returned to Levski Sofia, signing a contract till the end of the season with an option to be extended for two more years.

He played as the main custodian for Bulgaria during the 2014 World Cup qualifiers,[14] while Vladislav Stoyanov was selected for the last two matches - against Armenia and the Czech Republic.