[2] The first definite mention of the old grammar school is found in a deed dated 4 August 1469, when the Abbess of Syon granted to John Gardyner, of Bailrigg (near Lancaster), a lease of a water-mill on the River Lune and some land nearby for two hundred years to maintain a chaplain to celebrate worship in the Church of St. Mary, Lancaster, and to instruct boys in grammar freely, "unless perchance something shall be voluntarily offered by their friends".

This building (now known as Old School House), which stands on the north side of East Road, was designed by the local architects Sharpe and Paley at a cost of £8,000 (equivalent to £1,100,000 in 2023).

The downgrade from "outstanding" sparked controversy in the local and national community, and was received as part of a wider wave of downgrades in the inspection status of some of the UK's top Grammar Schools after the inspection exemption for "outstanding" schools was removed.

Nonetheless, the school has produced some notable figures in rugby union such as the former England and Bath coach Brian Ashton, former captain of Norway Erik Lund and his brother the England international Magnus Lund.

Jason Queally, took track cycling gold in the 1 km time trial at the 2000 Summer Olympics and Scott Durant won gold with the British Men's Eight in the 2016 Summer Olympics (see Boat Club).

In 2011, the LRGS lst XI won the Local Football Cup, beating Morecambe High School 1–0 at the Globe Arena.

In 2014, the LRGS 1st XI cricket team became the first in the school's history to win the RGS Festival.

The trophy was contested in Newcastle over a week of fixtures, and LRGS finished without losing a game in the tournament.

In 2010, the 1st XV, won the Lancashire Cup Final, and became champions in a match against Merchant Taylor's Crosby.

This achievement was followed by the U14s and the U15s who were victorious in finals against Merchant Taylor's Crosby and Manchester Grammar School, respectively.

In 2009, the U13s and U14s reached the finals of the Lancashire Cup, however both lost narrowly against Manchester Grammar School.

In recent years the school has enjoyed an improved reputation in cricket with recent highlights including the school's 1st XI Cricket team's narrow defeat in the Sir Garfield Sobers Tournament at The Kensington Oval Barbados in July 2011.

[18] His successor Peter Jago coached OL Scott Durant[19] who was member of the Great Britain Eight that won gold in the 2016 Olympic Summer Games.

Scott started rowing at Lancaster Royal Grammar School aged 15 with his twin brother Mason.

In 2010 LRGS won the Northern School Cross Country Championships for the first time, and repeated this feat in 2011 and 2012.

The Contingent, as of 2019 maintains around 200 members, and is led by a Cadet RSM, which can be drawn from any section (though typically of the Army).

Its roots, however, can be traced back further still, as there are "references to the existence at Lancaster of a Cadet Volunteer Battalion in the early nineteenth century".

[20] and in 1861, the seventy-strong Battalion was presented with a silver bugle "by Mrs Lee, wife of the Headmaster".

The main activities offered are water-based, and the section sails on Marine Lake, Southport.

Cadets in the Navy section also attend national camps and courses run by HQ CCF RN, on which cadets can gain nationally recognised qualifications in topics from power boating to first aid.

They participate in camps throughout the year including an annual camp that lasts over a week, and an Easter Camp where they take part in adventurous training activities, a range day where the cadets fire the L98-A2 Cadet GP Rifle, a field day where the cadets deploy on Manoeuvers for 24hours equipped with blank rounds and a night navigation exercise named Operation Night Owl.