Karl Tersztyánszky was born on the 28th of October 1854 at Szakolcz. For some unknown reason his records in the class book of the Military Academy at Wiener Neustadt show the date as the 21st of November and other official records show the 23rd of October but the original church register clearly gives the correct date of birth as the 28th of October 1854. He came from an old Hungarian noble family which owned some estates in the comitate of Neutra. In the 13th century the family had been granted the village of Nádas by the Hungarian King Albert IV and henceforth carried the predicate "von Nádas" since that time. After a private education at the estates of his father Karl he entered at the age of 10 the Gymnasium at Olmütz, which he passed with "very good success". After graduating from the Militärkollegium at St.Pölten with "excellent success" he entered the Military Academy at Wiener Neustadt. As the best of his age class he was promoted to Leutnant in dragoon regiment number 8 at Przemysl on the 1st of September 1877. After attending the Kriegsschule at Vienna with "very good success" he was promoted to Oberleutnant on the 1st of May 1882 and attached to the general staff corps where he received his promotion to Hauptmann 1st class on the 1st of August 1886. For his performance at the headquarter of the 2nd corps command he received a certificate of commendation from the corps commander in 1887. In the same year Karl Tersztyánszky von Nádas married, paying his prescribed Heiratskaution of 24.000 Gulden but this marriage remained childless. In 1888 he received another commendation from the headquarter of the 2nd corps. In 1891 he became chief of the general staff of the cavalry division at Jaroslau. During the year 1892 he received a certificate of commendation from the headquarters of the 8th corps, the Prussian Order of the Crown 3rd class and finally his promotion to Major on the 1st of November 1892. On the 1st of May 1895 he was promoted to Oberstleutnant. If one looks at Tersztyánszky's evaluations it can be seen that all his commanding officers were impressed by his knowledge's, intelligence, enterprise and fine character but were concerned a little with regard to his hot temper. It seems that with age this flaw became harder for him to control.
In spring 1896 Oberstleutnant Tersztyánszky assumed command of the officers' school of the brigade at Neu Zuczka and was transferred to hussar regiment number 14 at Nyiregyhaza. On the 5th of May 1897 he took over command of dragoon regiment number 1 at Tarnopol. In 1896 and in 1897 he received certificates of commendation from the war ministry. He received his promotion to Oberst on the 1st of May 1898 with seniority from the 19th of May of the same year. As a common routine he was awarded the Order of the Iron Crown 3rd class on the 13th of October 1901. It is remarkable that Oberst Tersztyánszky had received more commendations than similar senior officers but neither received a Signum Laudis nor the military merit cross. Perhaps his hot temper which lead to permanent quarrels especially with the administration had prevented him receiving any higher awards. In September 1903 he was appointed to the command of the 8th cavalry brigade followed by his promotion to Generalmajor on the 1st of November 1904. Again it seems strange that an officer with so many commendations and excellent annual evaluations by his commanding officers needed nearly 30 year on duty to reach this rank. For his excellent performance as the commander of this brigade he again received a certificate of commendation from the headquarter of the 13th corps in 1907. In July 1907 he was appointed to command the 2nd cavalry division at Preßburg (Pozsony) where he received his promotion to Feldmarschall-Leutnant on the 1st of November 1908. On the 25th of February 1910 he was honored with the award of the knight's cross of the Order of Leopold. In April 1910 Tersztyánszky took over command of the 14th infantry division also located at Preßburg. In September 1912 he was appointed commander of the 4th corps and commanding general at Budapest. During the year 1913 he was honored with the titles of Geheimer Rat (Privy Councillor) on the 2nd of April and Oberstinhaber of hussar regiment number 8 on the 21st of December. On the 1st of May 1913 he received his promotion to General der Kavallerie with seniority from the 30th of April 1913. In early 1914 he received the Papal Merit cross "Pro ecclesia et pontifice".
When the war started in 1914 Tersztyánszky's corps became part of the 2nd army along the river Save. The campaign as whole was a failure but the 4th corps archived a successful relief attack in support of the 5th army. In September 1914 Tersztyánszky and his corps were transported to the Russian theatre where they took part on the attack of Wereszyca on the 8th and 9th of September 1914. On the 9th of September he additionally took over command of the 7th corps and with both corps he was involved in the battles against much superior Russian forces near Lemberg. In October 1914 he was able to capture the important Uzsok Pass and finally took Turka on the 10th of October. The successful advance was stopped in the main by the superiority of the Russian forces. For his successful leadership he was honored with the award of the Grand cross of the Order of the Iron Crown with war decoration on the 5th of October 1914. On the 28th of October 1914 the 2nd army including Tersztyánszky and his corps was transferred to Prussian Silesia. During the following fighting, especially the battles near Szczecow, General Tersztyánszky performed well but considering the great superiority of the Russian forces an offensive success was not possible. He received the Prussian Iron Cross 1st and 2nd class and the 1st class of the merit decoration of the Society of the Red Cross with war decoration on the 31st of May 1915. In Spring 1915 General Tersztyánszky was appointed to plan the new offensive against Serbia and therefore he took over command of the troops along the Danube-Save line - renamed as Armeegruppe Tersztyánszky - on the 22nd of May 1915. During the following month he developed the full operational plan for the attack and effectively trained his troop for the coming campaign finally forming them into the new 3rd army. However the credit for his efforts would be enjoyed by General Kövess because Tersztyánszky's hot temper once again struck and caused his relief from the command of 3rd army. His employment of civilian workers with the army in the field he caused a major quarrel with a commissioner of the Hungarian government which soon reaching a damaging level. The Hungarian regional commissioner reported the dispute to the Hungarian prime minister Graf Tisza who in cabinet demanded the relief of General Tersztyánszky. Chief of Staff Conrad attempted to help him but the Hungarian prime minister was a too powerful enemy and at last Tersztyánszky was removed in September 1915 and sent on extended leave.
For his efforts in planning and training for the successful offensive against Serbia he received the grand cross of the Order of Leopold with war decoration on the 4th of November 1915. On the 1st of May 1916 he was promoted to Generaloberst with seniority from the 11th of May 1916. It would take some time before he would again receive a field command and again his temper adversely affected his career! In June 1916 Conrad von Hötzendorf searched for a commanding General who would not "be intimidated by the German leaders and rude enough to enforce our own interests" and found Generaloberst Tersztyánszky. On the 7th of June 1916 he took over command of the 4th army. His first mission was to support General der Kavallerie Georg von der Marwitz's "Armeegruppe" during the new counter attack at the end of June 1916. During this new offensive the 4th army received very heavy causalities and was not able to reach the objective of Luck. In July and August 1916 the 4th army got into very critical situations during the Russian counter attacks at Luck and Kowel and again sustained very heavy causalities. After receiving new troops the 4th army performed reasonably during the autumn Russian offensive especially at Swincky, Kortytnia and Zaturcy before the fighting wound down due to exhaustion on both sides. On the 17th of October 1916 Generaloberst Tersztyánszky was honored with the award of the Military Merit Cross 1st class with war decoration. When the swords were introduced he received these retroactively for all his previously awarded decorations and on the 17th of March 1917 he received the commendation of the Kaiser for his outstanding performance as the commander of an army which allowed him to wear the bronze Military Merit Medal (Signum Laudis) with war ribbon and swords. Shortly before he had received the grand cross of the Prussian Order of the Red Eagle with swords. This successful performance kept him from retirement because his hot headed character again brought him into trouble, this time with the German Generaloberst von Linsingen - both of them not really known for their diplomatic characters! The German headquarters demanded Tersztyánszky's removal and finally he was replaced by Generaloberst Kirchbach and took over command of the 3rd army in Galicia on the 19th of March 1917. But now his luck had left him. He tried to stop the Russian offensive at Stanislau and Klausz but on the 10th of July 1917 the superior Russian forces were able to break through and pushed back the 3rd army about 20 kilometres. The lost area was recaptured back some days later but this could not help, Generaloberst Tersztyánszky was removed from command on the 12th of July 1917.
The Kaiser did not want to retire the old veteran and suggested to him that he command the Hungarian Noble Lifeguard but Tersztyánszky refused this honorable post. He wrote a long letter to Generaloberst Bolfras listing all the reasons why he could not perform well at such a court post. Besides his well known troubles with the Hungarian administration and Graf Tisza he appended a long list of persons who had had problems with him since his time as the commanding general in Budapest and finally he put forward his great lack of knowledge of the Hungarian language! To avoid any further troubles Generaloberst Tersztyánszky was then appointed commander of the Leibgarde Reiter Eskadron at the court in Vienna. Shortly before he received the Merit Star of the Society of the Red Cross on the 11th of August 1917. After his final retirement on the 1st of December 1918 he lived in Vienna where Generaloberst Karl Tersztyánszky von Nádas died on the 7th of March 1921.