Only following the annexation of Thessaly in 1881 did both expand enough to warrant the establishment of regimental-sized units, and on 26 June 1885,[2] by royal decree, the 27 available battalions were formed into nine regiments.

[3] During the Greco-Turkish crisis of 1886, the regiment was ordered into Thessaly, but owing to the extremely poor state of the transportation network and the lack of sufficient means, the move proceeded very slowly, with only one battalion reaching as far as Thebes, and another Livadeia.

During the war in Thessaly, which was disastrous for Greece, the regiment fought in the battles of Mati, Domokos, Farsala, and Taratsa.

[3] In the lead-up to the First Balkan War, the regiment was mobilized on 17 September 1912, again as part of the 2nd Division, in the Army of Thessaly.

The latter participated in operations in the directions of Delviniko, but by February 1913 the entire regiment was gathered, as part of the 2nd Division, before the Ottoman fortified position of Bizani, that covered the city of Ioannina.

The regiment held the sector of the Avgo height, at the centre of the Greek front for the Battle of Bizani.

[3] With the outbreak of the Second Balkan War against Bulgaria, the regiment was the first Greek unit to go into action, being tasked with neutralizing the Bulgarian garrison in Thessaloniki.

The regiment then followed the general advance of the Greek army into Bulgaria through the Strymon River valley, capturing Strumica and Gorna Djumaya, where the armistice of 18 July found it.

On the same day, the 2nd Battalion likewise abandoned its exposed position and returned to the vicinity of Odessa, where it came under the command of the 7th Infantry Regiment.

[3] After the withdrawal from southern Russia, the regiment landed at Smyrna on 5 July 1919, moving to quarters in Turbali, and thence to Ayasoluk (near ancient Ephesus).

[3] The regiment participate din the March 1921 offensive, fighting battles at Dumlupınar, Bal Mahmud, and advancing to Afyonkarahisar.

With the renewed Greek successes at the Battle of Kütahya–Eskişehir, the regiment resumed its advance on 8–15 July, reaching the villages of Saltıdere and Maradji.

[3] Following the decisive Turkish victory at the Battle of Dumlupınar, on 30 August 1922 the regiment began to retreat towards the western coast of Asia Minor.

Marching via Sardis and Nif, it reached the port of Çeşme, where it embarked for the Greek islands of Chios and Lesbos on 3 September.

[3] Following the end of the Asia Minor war, the regiment remained in Athens, as part of 2nd Infantry Division, throughout the interwar period.

The 1st Regiment quickly reached its full strength, and on 1 November sailed from Elefsina to Volos, to be used as a reserve for the Greek army fighting in Epirus.

The regiment retreated via Moscopole, Erseka, Konitsa, and Zagori, reaching Metsovo, where it was ordered disbanded after the capitulation of the Greek army in Epirus to the Germans (21 April).

[3] From April 1946, the brigade participated in clean-up operations against the Communist guerrillas, in the first stages of the Greek Civil War.

Placed again under 2nd Division, the brigade participated in the decisive second battle of Grammos (Operation Pyrsos) in August 1949, which ended the civil war with the defeat of the communist Democratic Army of Greece.