AbstractSingle‐component ambipolar polymers are highly desirable for organic electrochemical transistors (OECTs) and integration into complementary logic circuits with reduced process complexity. However, they often suffer from imbalanced p‐type and n‐type characteristics and/or stability issues. Herein, a novel single‐component ambipolar polymer, namely, gIDT–BBT is reported based on indacenodithiophene (IDT) as the electron donor, benzobisthiadiazole (BBT) as the electron acceptor and oligo ethylene glycol (OEG) as the side chain. Benefitting from the extended backbone planarity and rigidity of IDT, pronounced electron‐withdrawing capability of BBT, favored ionic transport from OEG together with vertical OECT device structure, a nearly balanced ambipolar OECT performance is achieved for gIDT–BBT, revealing a high transconductance of 155.05 ± 1.58/27.28 ± 0.92 mS, a high current on/off ratio >10⁶ and an excellent operational stability under both p‐type and n‐type operation conditions. With gIDT–BBT in hand, furthermore, vertically stacked complementary inverters are successfully fabricated to show a maximum voltage gain of 28 V V⁻¹ (V_IN = 0.9 V) and stable operation over 1000 switching cycles, and then used for efficient electrooculogram recording. This work provides a new approach for the development of ambipolar single‐component organic mixed ionic–electronic conductors and establishes a foundation for the manufacture of high‐performance ambipolar OECTs and associated complementary circuits.