Rabbi Horowitz was born in Prague around the year 1565. As a young man he served as Rabbi of Cracow and other congregations before he was appointed as the Rabbi of the community of Frankfurt on Main in the year 1610.
He had attained such an outstanding reputation by that time that the contract offered him included the princely salary of 400 Thalers. His reputation may have been based on the glossary he wrote on his father's work עמק ברכה, and his achievements in well known communities.
His predecessor received a salary of 50 Thalers annually. He was to preside over litigation between members if the dispute concerned objects worth more than 20 gold pieces. The community undertook to secure citizenship of Frankfurt for the Rabbi's married children, failing which travelling expenses to Austria would be provided for them. His major work, something which must have occupied him for many years, was the שני לוחות הברית, a work which explores all aspects of the written and oral Torah. The part on the written Torah which this editor has translated comprises approximately 30% of the total monumental work.
Rabbi Horowitz also compiled an edition of the prayer-book with a comprehensive commentary. Many of his innovations have become part and parcel of the Ashkenazi Siddur. The present formulation of the Kol Nidrey prayer is but one of many that he has formulated anew. One of his outstanding talents was his ability to establish a logical connection between subject matters which to many seemed to lack such a connection.
From responsa literature signed by Rabbi Horowitz and dated in Frankfurt, it seems that he remained there till the pogrom of Vincent Fettmilch in the year 1616.
Rabbi Horowitz moved to Prague where he became the Chief Rabbi of the city. He moved to ארץ ישראל about 1621. He encountered difficult times there, especially in the year 1625. He was rabbi In Tiberias and died in or about 1630.
A full biography and discourse on the Life and Teachings of Rabbi Isaiah Horowitz by Rabbi Eugene Newman has been published in London in 1972 Rabbi Newman is Rabbi of the Dunstan Rd Synagogue in Golders Green, London.