Rubuta ci gaba ga wannan sakin layi - ya zama memba na IMRO. A cikin 1900 ya zama sakatare a cikin rukunin Andon Kyoseto, kuma a cikin 1901 Dechev ya kasance mataimakin voivode na Hristo Chernopeev a yankin Gorna Dzhumaya. A cikin 1901, tare da Hristo Chernopeev da Yane Sandanski, ya shiga cikin sace Ellen Maria Stone. A cikin 1902 an nada Dechev voivode na Veles, inda rundunarsa ta shiga cikin Afrilu kuma ta kafa cibiyoyin kwamiti. Ya yi adawa da ayyukan 'yan tawaye masu goyon bayan Serbia a yankin kuma ya shiga cikin fadace-fadace tare da su. Bayan yanke shawara don tayar da Ilinden a watan Janairun 1903, Nikola Dechev ya isa Bulgaria. A Sofia ya gana da Hristo Tatarchev da Hristo Matov, sannan wakilan kasashen waje na IMRO. Ya kuma koma Stara Zagora, inda ya sadu da shugaban IMRO Ivan Garvanov. A watan Maris na 1903 ya tafi Kyustendil, inda aka kafa rukunin Veles na biyu a ƙarƙashin ikonsa. Ya shiga Makidoniya, inda a watan Afrilu aka yi babban yaƙi da rundunar sojojin Turkiyya. Bayan babban asarar da rundunar Nikola Dechev ta yi, sai ya koma Bulgaria. A lokacin rani na wannan shekarar, ya shiga cikin Ilinden-Preobrazhenie Uprising
, yana ƙoƙarin shiga cikin Macedonia tare da sabon rabuwa a watan Satumba. A ranar 25 ga Satumba, an kewaye su kuma sun yi yaƙi mai tsanani kusa da ƙauyen Lukovo (Kratovo). A cikin yaƙin da dubban sojojin Turkiyya suka yi, sama da mutane 30 suka mutu, ciki har da Dechev, sauran kuma sun janye da daddare zuwa iyakar Yariman Bulgaria.