Whilst in Vienna Moscheles was able to meet his idol Beethoven, who was so impressed with the young man's abilities that he entrusted him with the preparation of the piano score of his opera Fidelio, commissioned by his publisher Artaria. At the end of his manuscript, before presenting it to Beethoven, Moscheles wrote the words Fine mit gottes Hülfe (Finished with God's help). Beethoven approved Moscheles's version, but appended the words O Mensch, hilf dir selber (O Man, help thyself!). Moscheles's good relations with Beethoven were to prove important to both at the end of Beethoven's life. (See below).
This is a family the like of which I have never known. Felix, a boy of fifteen is a phenomenon. What are all prodigies compared with him? ...He is already a mature artist. His elder sister Fanny [is] also extraordinarily gifted.
A couple of weeks later, he wrote:
This afternoon... I gave Felix Mendelssohn his first lesson, without losing sight for a moment of the fact that I was sitting next to a master, not a pupil.
Thus began a relationship of extraordinary intensity which lasted throughout and beyond Mendelssohn's life (he died in 1847). Moscheles was a major instrument in bringing Felix to London for the first time in 1829 - Abraham entrusted Felix to his care for this visit. Moscheles had carefully prepared for it. In London, apart from becoming a regular successful performer and a musical adviser for the soirées of the Rothschilds, he had become an invaluable aid for Sir George Smart and the Royal Philharmonic Society, advising them of the talents of European musicians he encountered on his own concert-tours. When Smart himself toured Europe in 1825 looking for new music and musicians for the Society, Moscheles furnished Smart with a list of contacts and letters of introduction, including both Beethoven and Mendelssohn. (In Prague, Moscheles's brother acted as Smart's guide). Smart visited the Mendelssohns in Berlin and was impressed with both Felix and Fanny. This eventually led to Mendelssohn's invitation to conduct at the Society on his 1829 visit.
In 1827 Moscheles acted as intermediary between the Philharmonic Society and the dying Beethoven. He helped persuade the Society to send Beethoven desperately needed funds during the composer's illness. In return Beethoven offered to write for the Society his Tenth Symphony. It was never completed.
Mendelssohn's great success in England from 1829 until the end of his life also reflected well on his friend. Although Moscheles's music was now being looked on as a little old-fashioned, he was heavily in demand as a music teacher and included amongst his pupils many children of the rich and aristocratic classes. He was also appointed 'Pianist to Prince Albert', a sinecure which nevertheless confirmed his status.
Moscheles never ceased to promote the music of Beethoven and gave many recitals of his music: in 1832 he conducted the London premiere of Beethoven's Missa Solemnis and he translated A.F. Schindler's biography of Beethoven into English. He was an early exponent of the piano recital - the concert of music for piano alone, the innovation of which is disputed between Liszt and Moscheles. Moscheles notably reintroduced the harpsichord as a solo recital instrument. He also often performed in concert with Mendelssohn in London (and elsewhere) - one great favourite of both musicians were Bach's concerti for multiple keyboard instruments. On these occasions Mendelssohn and Moscheles were renowned for vying with each other in impromptu cadenzas. Performances of the three-harpsichord concerto were given, on one occasion with Thalberg at the third keyboard, on another with Clara Schumann. Moscheles often appeared as a conductor, especially of Beethoven.
The Conservatory became in effect a shrine to Mendelssohn's musical legacy. The critic and pianist Edward Dannreuther, who studied under Moscheles at Leipzig between 1859 and 1863, later wrote:
[…] it was whispered that the two old Grands in the pianoforte-room of the Conservatorium were wont to rehearse Mendelssohn’s D minor Concerto all alone by themselves, from 12.30 on Sunday night until cock-crow! Force of habit, probably.
It thus fell to Moscheles to lead the counter-attack on Wagner after the latter's snide attack on Mendelssohn (and Meyerbeer) in his notorious article Das Judenthum in der Musik ("Jewry in Music"), which he did by requesting the resignation from the conservatory's board of Wagner's editor, Brendel. Like Mendelssohn, Moscheles believed that music had reached its Golden Age during the period Bach to Beethoven, and was suspicious of (although not necessarily antagonistic towards) new directions such as those shown by Wagner, Liszt and Berlioz. Nevertheless his personal relations with all of these (except perhaps Wagner) remained cordial. The Mendelssohn legacy in Britain meant that the Leipzig Conservatory had a high reputation amongst English musicians and amongst those who studied there during Moscheles's time were Arthur Sullivan and Charles Villiers Stanford.
Moscheles died in Leipzig on 10th March 1870, nine days after attending his last rehearsal with the Leipzig Gewandhaus Orchestra.
Among his 142 opus numbers, Moscheles wrote a number of symphonic works. Apart from an overture and a symphony, all are scored for piano and orchestra: eight piano concertos (of which the last has only come down to us in fragmentary form, no orchestral parts having survived) and sets of variations and fantasias on folk songs. The main theme of the finale of his fourth piano concerto is based on the tune, British Grenadiers.
Moscheles also left several chamber works (including a piano trio that has been recorded), and a large number of works for piano solo, including sonatas and the etudes that continued to be studied by advanced students even as Moscheles's music fell into eclipse. There are also some song settings.
In the last decade, with the modest but noticeable revival of interest in compositions by this composer and those of his colleagues, more of Moscheles's works are being made accessible on compact disc, especially by small and independent record labels. All the completed piano concerti and fantasias for piano and orchestra are available on the Hyperion Records label, played by Howard Shelley who also conducts the Tasmanian Symphony Orchestra; they have also issued the complete piano studies, played by Piers Lane. Ian Hobson has also recorded the first six, and included a pair of variations not recorded by Shelley.