The present invention provides a process for preparing a terpyridine compound of the formula I by obtaining a C1-C4-alkyl pyridine-2-carboxylate derivative by acid hydrolysis of a 2-cyanopyridine derivative by means of an anhydrous inorganic acid or its anhydride in the presence of water and a C1-C4-alkanol, with an equimolar amount of water being added to the 2-cyanopyridine derivative prior to addition of the anhydrous inorganic acid or its anhydride, subsequently condensing the resultant C1-C4-alkyl pyridine-2-carboxylate derivative with acetone in an aprotic solvent in the presence of a base, then reacting the obtained 1,5-bis(2-pyridyl)pentane-1,3,5-trione derivative with ammonia or ammonium salts (NH4)qY with removal of the water of reaction formed by employing a C1-C4-alkanol as an entrainer, and finally chlorinating the resultant 2,6-bis(2-pyridyl)-4(1H)pyridinone derivative in the presence of phosphorus oxide chloride.