He was a member of the House of Jelačić and a noted army general, remembered for his military campaigns during the Revolutions of 1848 and for his abolition of serfdom in Croatia.

[4] On the 11th of March 1819 Jelačić joined the Austrian army with the rank of lieutenant in the Vinko Freiherr von Knežević Regiment, named for his uncle.

Consequently, Jelačić's reputation differs in Austria where he was looked upon as a rebel seeking to break up the Austrian Empire, while in Croatia he is deemed a national hero.

[6] The Austrian Imperial Court initially opposed this act as one of disobedience and separatism, declaring him to be a rebel and the Sabor to be illegitimate.

The Sabor strongly opposed the "massive nationalist Magyarization politics of the Kingdom of Hungary from the Carpathians to Adria, which the newly formed government represents, especially Lajos Kossuth.

"[citation needed] On 8 April Jelačić took his oath as ban and was appointed a field-marshal-lieutenant and made commander of the Military Frontier.

Its scope of authority covered ministerial tasks including Internal Affairs, Justice, Schools and Education, Religion, Finance, and Defense, so this council was acting as a governing body in Croatia.

During his travels back to Zagreb, Jelačić read in the Lienz railway station that on 10 June the Emperor had relieved him of all his positions.

But Jelačić was still loyal to the Emperor, and kept relations with the Imperial Court, especially with Archduchess Sophia, the mother of Franz Joseph I of Austria.

During these, Jelačić stated that his position was derived from the Pragmatic Sanction of 1713, while Lajos Batthyány called him "a separatist" seeking to break away from the Habsburg Monarchy.

In August, Jelačić proclaimed a decree for the Croatians, where he denied accusations of separating Croatia in the name of Panslavism.

In the decree he said Being a son of the [Croatian] nation, being the supporter of liberty, and being subject to Austria, I am faithfully committed to the constitutional Emperor of the Empire and its Kings, and I long for a great, free Austria[citation needed] His closing words were: The Hungarian Government, as it is evident, would not like to agree on this; they insist on their separatist moves, which means they struggle to dismantle our Empire.

[citation needed] Jelačić felt disorder growing in the Austrian Empire, and decided on immediate action.

During his march toward Pest and Buda (now conjoined as the towns of Budapest), Jelačić got a message from Archduke Stephen, situated in Veszprém, to inform him of the decision of the Emperor that Lajos Batthyány was approved to set up a new government, and calling him to stop the troops, and to discuss further actions at his office.

According to Austrian sources,[citation needed] advisors to Jelačić persuaded him not to attend, because of a threat of assassination by agents of the Hungarian Government.

[14] The same day the Emperor appointed lieutenant-general Count Franz Philipp von Lamberg as general commanding all troops in Hungary, but this was annulled by the Hungarian Parliament.

Lajos Kossuth called the Hungarians for resistance, and the Országos Honvédelmi Bizottmány (National Homeguarding Committee) was given the power of execution.

[15][16] After his defeat at the Battle of Pákozd, on 30 September Jelačić asked for a three-day ceasefire; he wanted to use these days to wait for Roth's army.

On 4 October, Ferdinand I of Austria reappointed Jelačić as the general commander of all troops in Hungary, and dissolved the Hungarian Diet.

Led by General Karl von Zeisberg [de], the attack pushed back the Hungarian forces and defeated them.

Kossuth nominated Henryk Dembiński to replace Artúr Görgey, and started a strategic counterattack but was defeated near Kápolna.

On 14 July Hungarians took control over Feketić and Lovćenac, defeating Jelačić in the Battle of Hegyes and forcing him to retreat.

After Timișoara fell, Jelačić joined Haynau's troops, and after the end of the revolution, he travelled to Vienna to take part in discussions of reorganising Croatia, Slavonia and the frontier regions.

After the war the Empire's new constitution stripped the local authorities in Hungary of their political power, but this punishment also affected Croatia despite its assistance to the imperial cause during the revolution.

In 1851, when Baron Alexander von Bach came to power in the Kingdom of Hungary, Jelačić worked under him and made no objections to the Germanization of Croatia.

In his time and shortly after, Jelačić was a fairly unpopular figure among the Croatian political elite, including Ante Starčević and others, and especially among the people who suffered losses due to his military campaigns and had little benefit from his economic measures.

[1][22] In 2020, the home in which Jelačić was born was returned to the Croatian minority to be used as a cultural centre after being purchased by the Serbian government.

[23] It was officially opened on the 219th anniversary of Jelačić's birth in a ceremony attended by the President of Serbia Aleksandar Vučić and Croatia's Minister of Foreign Affairs Gordan Grlić Radman.

He is often referred to as "Jelasics the coward," who "runs back to Vienna with his army beaten", quote from Sándor Petőfi's poem A vén zászlótartó.

[29] Her father was an illegitimate son of Duchess Therese of Mecklenburg-Strelitz and her lover, Count Maximilian von Lerchenfeld-Köfering-Schönberg (1772–1809), which made him related to almost all European reigning families.