Nevertheless he went on tour as a pianist and received the Rubinstein Medal in Vienna. He gradually devoted more time to composition, but still performed, and in 1909 he was invited to join the conservatory faculty as a piano professor. A quiet person, he did not enjoy teaching, and resigned after a year, partly for that reason and partly to have more time for composition. In 1910, the wealthy conductor Sergei Koussevitzky invited Medtner to join the editorial board of his new music publishing firm, Editions Russe. He also made the acquaintance of Sergei Rachmaninov the same year. The two composer-pianists became close friends.
Medtner moved to Germany, but was repatriated when World War I broke out, with Russia and Germany on opposite sides. He felt it necessary to accept another teaching post in Moscow. In 1919 he married Anna Medtner (née Bratenshi), who had been the wife of his brother; the two of them suffered during the civil war and repression that followed the Bolshevik coup of 1917. In 1921 they were granted permission to tour abroad. They landed in Germany; aside from a 1927 tour they would never see Russia again. After a tour of the United States in 1925, they settled in Paris, which had the most important Russian emigré colony in Europe.
Medtner's music was harmonically adventurous, but had a Romantic aesthetic that was out of fashion in trendy Paris. Other locales welcomed his music more readily: he was acclaimed in the United States and Canada, and especially in England. His 1935 book The Muse and Fashion, published by Rachmaninov in Paris, expressed his disillusionment with modern music. The same year, Medtner moved to England. Failing health compelled him to give up concertizing in 1944, but he was able to make some classic recordings of his piano music through an arrangement set up by a newly formed Medtner Society, supported by the Maharajah of Mysore. These are outstanding examples of his superb playing technique and of his compositional intentions. He also made recordings of his songs, accompanying soprano Elisabeth Schwarzkopf. Medtner died at the end of a series of the heart attacks that gradually incapacitated him.
His output includes a few pieces of chamber music, over a hundred songs, and a large quantity of piano music, including a "Concert-Piece" and three concertos for piano and orchestra, his only works with orchestra. While there is a Russian flavor to his music, it really falls into the line of Schumann and Brahms, and he adopted the latter's interest in thematic unity. His canons and other contrapuntal works were well-planned, with inventive rhythms distinguishing the different lines. His harmonies tend to be low in the keyboard, giving his music a dark, brooding quality. He had strong opinions about the role of art, assigning it an almost religious role, and there is perhaps a spiritual purity to his music.Medtner was largely overlooked during the largely anti-Romantic twentieth century, but his music has recently enjoyed a sudden resurgence of interest.