Lorenzo the magnificent

He wrote the librettos for Mozart's three greatest operas - but that was just one extraordinary episode in the long and scandalous life of Lorenzo da Ponte

Why have they never made "Lorenzo da Ponte: the Motion Picture"? A life more mercurial, more cinematic is hard to imagine. It begins in 18th-century Venice; it ends in 1830s New York. With, somewhere in the middle, Mozart. And what a star part Da Ponte is - an enigma, equally at home in any country, any profession, any language, but ultimately seeming to belong nowhere. He was, after all, that rara avis, a Jewish Catholic priest with a wife and children. I see Alan Rickman; I see Sam Mendes; I see Oscars.

Pre-title sequence: a country road outside Sunbury, Pennsylvania, 1811. The odd clapboard house; picket fences. Music: Marriage of Figaro Overture, growing as a covered wagon trundles into view. Written on the side, "L de Ponty, Wagons". Waving from the driving seat is the eponymous Italian grocer (Rickman, aged up) delivering his latest batch of salami and parmesan. Girls in gingham wave back.

Or. Music: Don Giovanni Overture. Roman Catholic cathedral, New York, 1838. Candles; smoke; camera pan over a vast congregation then out on to the pavement. Passer-by to mourner: "Who was that guy?" To which the answer may have been "professor of Italian at Columbia College". Or "impresario" or "scholar" or "opera producer" or "head of important New York family". And if "librettist", then probably of his worldwide hit Una Cosa Rara, or possibly of the lesser-known Don Giovanni. Still, at least Giovanni had played New York. Figaro and Cosi fan Tutte had to wait a century or so.

So who was he? Well, for a start he wasn't even Lorenzo da Ponte. Another opening sequence. Ceneda, north of Venice (called, since 1918, Vittorio Veneto). Hebrew school in the busy ghetto. A rabbi teaching boys in skullcaps. Fourteen-year-old Emmanuele Conegliano and his brother Baruch are called from their studies by their widowed father, who introduces them to their new stepmother. Who is not only 16 but also - shock! horror! - a Christian. So Emmanuele, only recently bar mitzvah-ed, is summarily baptised. In those days converts, by tradition, took the surname of the local bishop, the eldest taking all his names. The bishop of Ceneda was called Lorenzo da Ponte. Such an extraordinarily violent deracination from family, faith and identity may go a long way toward explaining Da Ponte's subsequent peregrinations.

Under the tutelage of his namesake the bishop, Lorenzo entered a seminary and became a priest. Whereafter, as most smart young men did, he moved to Venice, a city for which the word "decadent" could have been invented. It was a place (and still is) where high and low life seemed to be synonymous with as many convents as brothels, with not a lot to differentiate the two. And with Carnival for half the year, where anything went if you were masked (cf Giovanni), where priests would hear confession from their fellow revellers in the morning. Da Ponte's professed professions at that time (priest, private tutor, professor of poetry and rhetoric) were in reality mere sideshows to the main strand of his life in and around Venice: that of libertine (cf Giovanni again).

Scandals followed swiftly, seductions, an elopement, an illegitimate child (given to the foundlings' hospital and probably taught the violin by Vivaldi), squibs and satires against the republic, accusations of sedition and blasphemy and, ultimately, banishment. Not before, however, he befriended the greatest libertine of them all, Giacomo Casanova (cf Giovanni, big-time).

Thankfully, it was possible, just, to earn a living as an Italian poet abroad. The secret was to acquire, and preserve, patronage. Da Ponte began in Austria, where he was soon composing odes of praise (in Italian) for German-speaking generals and translating French plays for Italian theatre companies touring Austria. (Il Conte de Warwick was an early hit.)

By a stroke of fortune he was led to Vienna, already home to several illustrious Italians. Most notable of them was Metastasio, the grand master of libretto-writing, then in his seventies, and the court composer, Salieri, who, whatever his subsequent reputation, was a great encourager of what he perceived to be talent. Both were seduced by Da Ponte's charm and both took him under their wing. Salieri recommended him to the emperor, and Lorenzo was appointed poet to the imperial theatres, charged with writing plays and libretti - with absolutely no experience whatsoever. When he explained as much, with some diffidence, to the emperor, the reply was: "Good, good, good. A virgin muse!" Not for long.

Da Ponte's first effort was, unsurprisingly, a disaster; his second, to music by Soler, hardly better. Da Ponte's stock was definitely on the wane. Which is when our hero had his brush with destiny. It was all Mozart's idea. They had met at parties and had got on well, despite having little in common. Da Ponte was, at least at that time, a dilettante. Mozart was a professional who had known little in life but hard work. A master of every aspect of his craft, he had been knocking around theatres from early childhood, whereas Da Ponte was still busking. But like the best buskers, he was learning on the job, and in a sense that was just what Mozart was after: a librettist skilled enough to versify and modest enough to shut up and listen, and learn.

To set the still-banned Marriage of Figaro was Mozart's idea; the way to condense it was doubtless also his. But the execution was all Da Ponte's. And, rather wonderfully, one can see him, nurtured and encouraged by a theatre genius, improving as the piece unfolds. By Act IV, by Susanna's amorous "Deh Vieni" and Figaro's vicious "Aprite un po", we see a true dramatic poet emerging from pretty much nowhere.

If Figaro is a miracle of concision, then Giovanni, their next opera - written the next year, 1787 - is a miracle of expansion. Da Ponte took on this occasion an existing libretto and wrote it up, which may explain why there are more static arias than in Figaro and less excitement in the second half. But that is hardly surprising in a show, a self-styled dramma giocosa, that begins with a rape and a murder in the first five minutes. By now Da Ponte was confident in his trade. Besides, he had a hit under his belt, Soler's Una Cosa Rara. (Indeed Da Ponte was convinced until his dying day that it was a finer work than any by Mozart.)

Their last collaboration was their least commercially successful and arguably Da Ponte's finest achievement. Cosi fan Tutte was again almost certainly Mozart's idea. Sex he adored; sisters he adored, too, having been engaged to a pair. The combination of the two proved irresistible. Add to the mix the fact that the two original sisters in Cosi were sisters in reality, and that Da Ponte was having an affair with one of them, and the piece looks more and more like a private confection.

Nevertheless, Cosi will, in its ruthlessly structured way, tell you more about love, lust and loyalty than you will learn in a lifetime - or certainly ever want to. But in 1790 no one seemed to care. Politics and revolution were in the air; Beethoven was around the corner, with Verdi and Wagner not far behind. There were wars to be fought and blood to be let, and it was not really until the 1920s that people had time and patience enough to examine the tiny but lethal crimes that we human beings can commit in the name of love.

Mozart died the next year, and Da Ponte left Vienna. But that is not the end of his story: he had almost 50 years left to live. I could tell you about his days as a bookseller in London or as a grocer in Pennsylvania. I could tell you of how he founded the first opera house in New York. Or even of how, when in Prague, he asked Casanova (who better?) to provide rewrites for the first run of Don Giovanni; or of how he had his portrait painted by Samuel Morse (inventor of the code); or of how a rival for a woman's attention laced his mouthwash with acid and made all his teeth fall out. It's all true - but for the details, you will have to wait for the movie.

All three Mozart/Da Ponte operas will be performed at Glyndebourne this season (01273 813813). 'The Marriage of Figaro' will be transmitted live on location on BBC2, throughout the day, on 29 May