In 1971 Malcolm McKelvey, the Director of Music at Christ's Hospital School situated 2 miles from Horsham, co-founded a small orchestra together with Horsham residents Christopher Herzig and Francis Phillips (both viola players) for the benefit of Horsham music-makers and the music loving public. It began modestly on a non-commercial basis with 2 concerts a year given in the town in school halls in aid of Horsham charities. The Orchestra was composed of amateur players. A small committee was formed with no constitution. It was called the Horsham Orchestra and adopted the heraldic lion of the Horsham District Council as the Orchestra's emblem. Rehearsals were held on Wednesday evenings at Christ's Hospital School. The leader, also a Horsham resident, was Lionel Rose who led the Orchestra for 20 years.

Malcolm McKelvey invited Trevor Hoskins, also from Christ's Hospital to become Associate Conductor. Later when Trevor Hoskins moved from the school Graham Standley, a young County Music Advisor for Wind Bands, assisted as Associate. The charity performances in schools and on one occasion in the TA Drill Hall in Denne Road, continued until the advent of the Horsham Arts Centre.

In 1985 when the Arts Centre opened its doors for the first time the Horsham Orchestra gave a concert there. This proved so popular that it was decided to move the concert and rehearsal venues permanently to the Arts Centre and to manage the Orchestra on a commercial footing. With a more attractive venue good players were soon attracted to the Orchestra. Young professional soloists were also engaged for their concerts when a local Horsham company, Ringway, became the Orchestra's first sponsor, continuing their sponsorship for 9 to 10 years.

The orchestra continued to give 2 concerts a year in November and May and when Malcolm McKelvey decided to retire he offered the Orchestra the choice between 2 promising ex pupils from Christ's Hospital, who had graduated with music degrees from Oxford and Cambridge, to be auditioned for the now vacant post of Musical Director. In 1989 Charles Hazlewood was selected and 3 and a half fruitful years followed for the Orchestra in having the benefit of his professional approach and choice of more ambititous repertoire. Lionel Rose who had led the orchestra for 20 years retired and Martin Palmer a young Horsham professional violinist was engaged as the leader. It was during Charles Hazlewood's last year as Musical Director that the Orchestra was renamed "the Horsham Symphony Orchestra" and the modern logo in use today was adopted. Paul Hoskins, a Cambridge music graduate, whose father Trevor had been Associate Conductor, took over the baton from Charles. It was Paul, building on the good foundations laid by Charles, who proposed that the Orchestra should give 3 concerts a year in March, May and November.

In June 1995 the Horsham District Council financed the first ever "Fanfare" Horsham District Arts Festival, which took place in the Horsham Arts Centre initially and the Orchestra was invited to give a concert and in so doing to accompany a newly formed Festival Chorus. Thus the third concert of the year was moved to June. In 1996 the Council, aided by Sainsbury's Art Fund, commissioned the sculptor Angela Conner to create a water sculpture in a purpose built square to celebrate the 200th anniversary of Shelley's birth. The sculpture was called the Rising Universe taken from the opening lines of Shelley's "Mont Blanc" poem. As a larger scale HSO music commission celebrating Shelley had already been proposed by an anonymous benefactor and Martyn Harry had been selected to write that piece, the Horsham District Council approached him to write a fanfare for the inaugural fountain ceremony to lead into ten further minutes of music to accompany the first inaugural water cycle of the fountain. HSO woodwind, percussion and brass players augmented by players from Christ's Hospital performed the "Mont Blanc" music with TV and newspaper coverage on November 13th in the new Bishopric square. Paul Foot, renowned Shelley scholar and journalist, gave the opening address.

During this period Paul Hoskins handed over the baton to Benjamin Pope, having auditioned for the post together with 2 other aspiring young professional conductors. Benjamin Pope finally took over from Paul in March 1997. Benjamin conducted the world premiere of 22 minute piece "Symphonic Shelley" by Martyn Harry in the Horsham Arts Centre in June 1997 in the second of the Horsham District Council's Fanfare Horsham District Arts Festivals. Benjamin enlarged and extended the orchestral repertoire still further and was HSO Musical Director for 10 years.

Ringway gave up the sponsorship of the orchestra in 1996 when Allied Domecq took over as sponsors, generously supporting the Horsham Symphony Orchestra until March 2002.

Since 1997 the Orchestra adopted a written constitution and registered as a charity. It is also a member of Making Music, the National Federation of Musical Societies. The Orchestra now has a Friends of the Horsham Symphony Orchestra scheme and a number of Patrons. It runs a Young Musicians' Bursary scheme to encourage young people to participate in playing orchestral music, helping them if they show commitment with a small one off grant, financed initially by Horsham businesses and latterly by a private patron.

At the end of 2001 the Arts Centre closed for refurbishment and the Orchestra moved to the Drill Hall for its concerts. The Arts Centre reopened on 13th September 2003 under the new name The Capitol. The Orchestra gave its first concert in The Capitol on 15th November 2003.

The Orchestra's current Musical Director is Steve Dummer who is taking the Orchestra through a very exicting period including its 40th anniversary, sell-out concerts at The Capitol, rave reviews and exciting and challenging new repertoire.