At an early age, he was violinist at the Polish Royal Chapel, after which he travelled to Vienna about 1785 to see and listen to Haydn and Mozart.
From Austria, he accompanied a Polish princess to Italy, to refine his artistic abilities with the Italian masters of that day, where he lived for three years.
In Paris, he appeared at the Concerts Spirituels in December 1787, and was described in the Mercure de France as a pupil of the Italian violinist Giovanni Giornovich and was immediately recognised by the Parisians as an artist of high rank.
There he was employed by the Duc d’Orléans and for a short time he enjoyed the pension of a musician on the establishment of Mlle.
[1] During the subsequent years he expanded his violin performances and musical pursuits to Manchester, Liverpool, and Ireland.
During several seasons Janiewicz played in London, visited the provinces and Ireland as a violinist, and conducted the subscription concerts in Manchester and Liverpool.