The club was officially formed on 21 November 1923 as Keravnos Piraeus (English: Lightning), but existed unofficially since 1922.

One year later the club was renamed to Young Boys Titan, after some players' secession that formed Peiraikos Podosfairikos Omilos (English: Piraeus' Football Group).

The club was renamed to Ethnikos (English: National) on 23 December 1924, after it merged with Peiraikos Podosfairikos Omilos.

Ethnikos was one of seven clubs, including AEK Athens, PAOK, Panathinaikos, Aris Thessaloniki, Olympiacos and Panionios, never to have been relegated from the league until 1990.

[3][4] From the break-up, one group, led by Giorgos Chatziandreou, brothers Kostas and Dimitris Ferlemis, and Christos Peppas, ultimately formed Omilos Filathlon Piraeus – Faliro (Greek: Όμιλος Φιλάθλων Πειραιώς – Φαλήρου), meaning Fans' Club of Piraeus and Faliro in 1924, and then changed the name to Ethnikos O.F.P.F.

in February 1925[3][4] the other group, led by Yiannis Andrianopoulos and his five brothers, formed the club that evolved into Olympiacos CFP in March 1925.

Prior to the Olympiacos match though, Ethnikos was disqualified from the championship, on the accusation of professionalism, as they had allegedly been in contact with Hungarian stars Ferenc Puskás, Zoltan Czibor and Sándor Kocsis.

Ethnikos was docked 4 points and not allowed to play the final 4 matches of the season, and Olympiacos took the championship.

Though never making another legitimate challenge for the league championship, Ethnikos remained consistently competitive during the 1970s, never finishing outside of the top 10.

Specifically, in the replay match, Ethnikos was playing roughly 60 minutes with 10 men and despite going 1–0 down at half time, managed to equalize at the last play of the match with a back header coming of the team's centre back Fotis Papadopoulos.

In 1986–87 Ethnikos made a very mediocre 10th-place finish, but late in the season earned one of their more memorable results– winning 6–3 away to Panathinaikos.

That year Ethnikos tried to make a run at a UEFA Cup berth, but ultimately fell short and finished 7th.

In the 1988–89 season Ethnikos made a good run in the Cup, reaching the Semifinals before being eliminated by Panathinaikos, but in the league the team finished in the bottom 3 and was relegated to Beta Ethniki for the first time in their history.

With time expiring, a free kickgoal from Eduardo Sander Da Silva against Messiniakos made the final score 1–1 and gave Ethnikos the point needed for promotion.

Ethnikos were placed in the Group 9 and relegated to the local amateur leagues at the 5th level of the Greek football pyramid, the lowest in their history.

Ethnikos won the double in the 2013/14 season (Piraeus champions and Cup winners), and finally managed to return to the third tier of Greek football through the promotion play-offs where they topped the Group 9.

Ethnikos did manage to win only one game against Dinamo Zagreb, as the star player of the team Washington Calcattera had been injured.

Ethnikos participated as newly promoted team (according to the competition new rule) and qualified automatically to the semifinals, but did not manage to secure a place in the final, though they came close to achieve it in the second leg.

When the new Karaiskakis was completed in 2004, Ethnikos was struggling in Gamma Ethniki, and did not move into the stadium; the team instead continued to play most of its home matches in Nikaia Municipal Gymnasium (2002–2005), a small stadium in the Nikaia area of Piraeus, which is the traditional home of Proodeftiki F.C.

Helliniko Olympic Complex in Ellinikon,[18] was located approximately 8 kilometres south of the center of Athens, near Glyfada on the Mediterranean coast.

[18] In 2013 AEK FC started talks with the Olympic Committee for using the stadium and increasing the capacity to 22.000, but there was no official offer.

Ethnikos continued playing at Elliniko for one more season and then moved to Moschato ground with wooden stands and capacity of 2,500 (2014–2017).

Ethnikos was scheduled to use the stadium for the 2023–24 second half of the season, competing at the third-tier of Greek football.

Later it was replaced by one with five blue and four white stripes having the club's name on the top of the badge, again resembling the Greek flag.

After the 2011 takeover of the club by Alexis Aggelopoulos, the logo was changed once again to a more "modern" looking one but with supporters's demand, the older one was restored.