Botev Plovdiv was allowed to participate in the UEFA Europa League despite finishing on 4th place of A Grupa during the previous season because of the financial troubles at CSKA Sofia.

During the European campaign Ognyanov scored two goals in the home wins against FC Astana and HŠK Zrinjski Mostar.

With four goals Marian shares the third place in the list of top goalscorers for Botev Plovdiv in the European football tournaments.

[21] On 23 September, Marian Ognyanov scored the second goal for the 0–4 away win against Lokomotiv Mezdra in the first round of the Bulgarian Cup tournament.

Ognyanov prove his creativity and passing abilities and was involved in both goals for the 0–2 away win in the derby match against the local rivals Lokomotiv Plovdiv.

[26] Ognyanov missed the game with CSKA Sofia due to a ban, and on 22 March he was again in the starting lineup for 0–0 draw with Ludogorets Razgrad.

[30] On 17 June, Mariyan joined the Romanian professional football club Târgu Mureș on a free transfer, but he left a week later for personal reasons and returned to Botev Plovdiv.

[33] Ognyanov missed the second round in A Grupa and returned in the starting lineup for the 1–1 draw against the local rivals Lokomotiv Plovdiv.

[34] On 22 November, Ognyanov made the assist for the winning goal scored by Nico Varela during the away game against Cherno More Varna.

[36] On 7 April 2016, Botev Plovdiv announced that the expiring contracts of Ognyanov and the goalkeeper Valentin Galev will not be renewed for the next season.

[37] A week later Nikolay Kostov, the head coach and manager of Botev Plovdiv at that time, explained that he expected better performance and more engagement to the development of the younger players from Mariyan.

[39] On 19 April Ognyanov received a medal of honor and special t-shirt to celebrate his 133 appearances in official games for Botev Plovdiv.

[45] Ognyanov made his debut for Bulgaria on 15 August 2013, after coming on as a substitute during the 0–2 defeat from Macedonia in a friendly match.