After managing
Spartak Plovdiv as a head coach for one season, he became an assistant at
Litex Lovech under
Ferario Spasov. He remained in this role for several years, followed by short spells at
Botev Plovdiv and
Sliven. He later briefly managed the latter during the
2010-11 A Group, but was unable to help them avoid relegation.
Ludogorets Razgrad On July 31, 2014, Dermendzhiev replaced
Stoycho Stoev as head coach at Ludogorets following the latter's disappointing 0-0 home draw against
Partizan Belgrade in a
Champions League qualifying match. On 27 August 2014, Dermendzhiev became the second Bulgarian manager (after
Stanimir Stoilov in
2006) to qualify a team from his country to the
group stage of the Champions League. On 22 October 2014 he became the first Bulgarian coach to achieve a win in the Champions League's group phase when Ludogorets beat Basel. He resigned from the team on 31 May 2015, but after Ludogorets was unsuccessfully led by his successors
Bruno Ribeiro and
Eduard Eranosyan, he was appointed again as manager on 6 November. In the
2016–17 Champions League Ludogorets won the qualifiers against
Mladost Podgorica and
Red Star Belgrade, and the play-off against
Viktoria Plzeň, respectively, thus becoming the first Bulgarian team to qualify twice for the
group stage of the tournament, both times with Georgi Dermendzhiev as a coach. Dermendzhiev resigned on 9 August 2017 after the team failed to win the
2017 Bulgarian Supercup.
Ordabasy On 9 January 2018 Dermendzhiev signed a deal with the
Kazakhstan Premier League team
Ordabasy. He left the position in June 2018.
Levski Sofia On 22 January 2019, Dermendzhiev returned to Bulgaria, being appointed as head coach of
Levski Sofia. He was released from his duties on 29 April 2019.
Bulgaria In October 2019, Dermendzhiev was appointed as head coach of the
national team to manage the side during the
remaining Euro 2020 qualifiers. In April 2020, his contract was extended for an additional six months, with the option for a further one year and a half. In December 2020, the
Football Union announced that Dermendzhiev will not continue in his position as manager after the national team failed to qualify for
Euro 2020 via the playoff route and
was relegated from League B to League C in the
Nations League. Dermendzhiev had previously faced strong criticism by Minister of Youth and Sports
Krasen Kralev due to the perceived failure to integrate more U-21 players into the senior team and the results attained, including the team's tendency to concede
last-minute goals.
Ludogorets Razgrad In October 2023, Dermendzhiev was appointed manager of
Ludogorets Razgrad for the third time. He successfully led the team to a 13th consecutive league title. In August 2024, Dermendzhiev stepped down as head coach following the club's elimination from the
Champions League by
Azerbaijani team
Qarabagh. ==Managerial statistics==