The last sonata in the set of Kv.301-306 is the Sonata in D major which has a grander scale and is said to be more meant for professional virtuosi of those time than the 'amateur' performers. This Sonata is the only one in the set which contains three movements and is written in the summer of 1778 during Mozart's trip in Paris. It was also the inspiration for a double concerto for violin-piano and orchestra. Unfortunately Mozart only wrote the first movement. Due to the fact that it is inspired by Kv.306.
The first movement starts with both instruments together, something that became common during his development of the violin-piano sonatas. The piano has the main line and the violin plays the same part as the piano. It is again a major virtuosic work for the piano but one can clearly see that both instruments get more equal parts. In the development section, Mozart used motives that he introduced before in the introduction. The development contains a similar impressive section like in the Sonata Kv.296 and is the biggest development in the whole set.
The second movement is a mature slow movement for which he is especially famous in his later works. It is the biggest slow movement for violin and piano that he wrote till then and gives the concerto-like feeling. It is written in an A-B-A style. Most of the thematic material is being introduced by the piano and repeated by the violin, as he often did in the previous sonatas but the instruments respond more to each other, thematically, like for example at the beginning of the B-section.
The third movement is an extremely difficult movement from the point of view of playing together. Both instruments clearly show a big virtuosity and especially the piano has very complex passages. The phrasing and articulation are written down very precisely, which shows that both instruments are supposed to match each other. A written out cadenza, at the end of the movement, for both instruments show that Mozart definitely had a concerto in mind when he wrote this sonata. Both instruments play very typical cadential material, like thrills and fast broken chords, although the piano has again the main part. The piece ends with the first theme.