Some successful people's names enter history, whether mightily or much more modestly, through dedication to a cause, be it spiritual or social, through a unique cultural contribution or through far-sighted patronage of worthy men.

Other names don't, and the reason can often be somewhat random, a combination of fashion, malign influences, of being on the wrong side of an argument, or being overshadowed by the extreme greatness of a collaborator or associate, or of not having paid sufficient attention to posterity in one's lifetime. Charles Jennens would seem to fit into this category, something a fascinating new exhibition at London's Handel House is seeking to address.

The name may well be familiar to readers here. After all, it was Charles Jennens who put together the text of one of the most performed of all choral works, Handel's Messiah (the oratorio may well even have been his idea), and he who wrote the libretto of Saul, Belshazzar, and possibly Israel in Egypt. But however familiar the name, he's hardly as well known as Da Ponte for instance.

Through exhibits and artefacts, Handel scholar and curator of the exhibition Ruth Smith has drawn us a rounded picture of the man, an exhibition every bit as interesting for presenting a genuinely intriguing 18th century figure as for adding to our knowledge of the world around Handel. Jennens turns out to be a prism through which a number of the cultural, religious and social issues and fault-lines of the time can be observed.

A landowner of considerable inherited wealth, his place in society was complicated by his status as a non-juror – someone who refused to swear an oath to the Hanoverian monarchy, thus excluding themselves from positions in politics, government, the law, the church or army. Despite the Roman Catholic connotations allegiance to the Stuart line might imply, Jennens was, like many fellow non-Jurors, a devoted Anglican, thus torn between allegiance to his faith and to what he held to be the correct lineage of kings. Charles I was unsurprisingly an inspiration and icon, and a detail from the frontispiece of the executed King and Martyr's Eikon Basilike formed Jennens's seal.

Civic service's loss was culture's gain. Jennens was a Handel devotee and patron, a self-acknowledged addict of the man's music, a collector of his scores as well as collaborator on some of the greatest works in the repertoire. He was that happy combination of taste, talent and significant money which helps enrich many an era. But Ruth Smith demonstrates he was more than a mere provider of words for a genius to set: his librettos themselves, not least in works such as Saul positively inspired Handel in his creative process. In works from Belshazzer to Messiah itself, his appreciation of where Handel's strengths lay - and how to get the best of him - led Jennens to fill the libretto with moments of very visual drama and images. Yet Jennens himself did not want to share in the glory - he simply wanted to further the great composer's success. The libretti were all given as gifts to Handel, and published anonymously.

Jennens was also a scholar, amassing a library of 10,000 volumes, offered an important contribution to Shakespeare studies (he was the first person to publish an edition of a single Shakespeare play with notes), was owner of one of the first pianos shipped to England, and even his house - sadly no longer extant - was remodelled under his guidance such that Pevsner later described it as the last great example of English Palladianism. The exhibition's choice of documents and artefacts illustrates all these facets of Jennens's life and work, its patronage and paradoxes: Handel scores open to reveal his contribution sit near silver mugs bearing the Fleur de Lys for toasting the 'King over the Water'.

What kind of person was Jennens? Several fine portraits assembled here characterfully tell us what he looked like, including a delicate drawing by Giles Hussey. Elsewhere we gain insights about his character - and also learn about an attack on his work and character which probably did more than anything to plunge him into relative obscurity. Charles Jennens turns out to have been a fascinating man. He was also, it seems, a good one who added to the world around him, and certainly one who deserves not to be forgotten.

'Charles Jennens: The man behind Handel's Messiah' is at London's Handel House until April 14, 2013