During the Battle of the Somme, three players gave their lives for king and country: Richard McFadden, George Scott and William Jonas.

Prior to the First World War and whilst on a training run, O's striker McFadden had saved the lives of two young boys who were drowning in the River Lea – this, only a week or so after rescuing a little girl from a house fire, when walking through Clapton Park on his way to the O's ground.

History was made on Saturday 30 April 1921 when the Prince of Wales, later to become King Edward VIII, visited Clapton Stadium/Millfields Road to see the O's play Notts County.

The royal visit was to show gratitude for Clapton Orient's patriotic example during the Great War and there is now a plaque erected on the site of the Millfields Road Stadium to commemorate this historic event.

In 1972 Orient achieved one of the most famous results in their history – coming back from 2–0 down to beat Chelsea 3–2 in the FA Cup fifth round.

However, the financial crisis at the club caused by then-chairman Tony Wood losing his business in the Rwandan Civil War led to a relegation back to the fourth tier, now renamed as the Third Division following the formation of the Premier League.

Orient's fastest ever goal was scored after just 12 seconds by Lee Steele in a match against his former club Oxford at The Kassam Stadium on 28 March 2005.

After Tommy Taylor left the club, Paul Brush spent two unsuccessful years in charge and after he was sacked, former player Martin Ling took over as manager in October 2003, with Orient second-bottom of the league.

This promotion season also saw an excellent FA Cup run, with Leyton Orient progressing to the fourth round after beating Premiership side Fulham.

Dean Beckwith put Hereford ahead before JJ Melligan and Adam Boyd gave Orient the win.

Orient then continued the season with multiple poor results and performances throughout September and October and their only wins were away matches against Walsall and Southend United in the Football League Trophy first round.

Two Goals from Jason Demetriou and Danny Granville in a 1–2 away victory against Bradford City put Orient through to the third round of the FA Cup where they played Sheffield United at home.

They lost 4–1 and, after a run of bad form in the league, Orient parted company with manager Martin Ling and assistant Dean Smith.

After Geraint Williams' positive influence on the team they secured their League One status on 13 April with a 1–0 win over Swindon Town at the County Ground and eventually finished the season in 14th place.

Orient had a proud day when they beat former Premier League runners-up Newcastle United 6–1 in a pre-season friendly match on 25 July 2009.

On 3 April 2010 Geraint Williams was sacked as manager after a 3–1 home defeat to fellow relegation strugglers Hartlepool following a poor run of form.

Kevin Nugent once again took control for the 2–1 defeat at Southampton on 5 April and after the match Russell Slade was named as manager until the end of the season.

After a poor start to the 2010–11 season, Orient's league form picked up towards Christmas, culminating in an 8–2 win against non-league Droylsden in an FA Cup second round replay.

Orient beat Swansea 2–1 to set up a glamour fifth round tie against Premier League giants Arsenal at Brisbane Road, which finished in a 1–1 draw thanks to a late Jonathan Téhoué equaliser for the O's.

A disastrous second half of the season meant that Orient was relegated from League One after a 2–2 draw at Swindon Town on the final day.

However, the following season (2016–17) saw another disastrous slump, under five different managers,[14] as well as off-pitch turmoil, including a winding-up hearing against Becchetti for unpaid taxes.

[15] Another managerial departure saw Daniel Webb resign from the club, with assistant manager Omer Riza taking over first-team duties until the end of the season.

[25] Orient's first season back in League Two produced a 17th-place finish, with the final table ultimately being determined on a weighted points per game basis because of football's suspension due to the COVID-19 pandemic.

[30] Jackett was sacked in February 2022 after a bad run of form which left the club only 3 points above the League Two relegation zone and was replaced by Richie Wellens who kept Orient up and secured a comfortable 13th-placed finish.

[35] The club shirt sponsorship deals have included tie-ups with Independent Transport, Acclaim Entertainment, Marchpole, Matchroom Sport and PokerMillion.com.

Millfields could hold 35,000 or more and was quite modern for its time, though larger crowds were typically for dog racing and speedway and was a major London venue for boxing and baseball.

Orient's next two home league fixtures (both victories) were held at Wembley Stadium, the second attracting a crowd of just 1,916 to see the 3–1 win over Southend United.

Notwithstanding that finance for the redevelopment had already been raised by selling off the four corners of the stadium for residential blocks of flats, an increase in costs meant that an emergency general meeting of the company was needed in April 2005.

The remaining five minutes of the game were eventually played three hours later behind closed doors, the protest brought much needed publicity to the club's plight, with worldwide news coverage.

Although they have not often played in the same division, they have met in the League Cup in 2011–12 season, Leyton Orient beating the Shrimpers after extra time on penalties.