As an English name, it was occasionally used during the Middle Ages in honour of the Old Testament heroine. It did not become common until after the Protestant Reformation, at which time it was often spelled Susan.
As a Christian name, Ruth has been in use since the Protestant Reformation. In England it was associated with the archaic word ruth meaning "pity, compassion" (now only commonly seen in the word ruthless). The name became very popular in America following the birth of "Baby" Ruth Cleveland (1891-1904), the daughter of President Grover Cleveland.
A famous bearer was the American jazz musician Nina Simone (1933-2003).
In the United States this form was more popular than the full form Elizabeth from 1958 to 1978, and was in fact the top ranked American name between 1962 and 1969.
In England, this Latin form has been used alongside the vernacular forms Ann and Anne since the late Middle Ages. Anna is currently the most common of these spellings in all English-speaking countries (since the 1970s), however the biblical form Hannah is presently more popular than all three.
The name was borne by several Russian royals, including an 18th-century empress of Russia. It is also the name of the main character in Leo Tolstoy's novel Anna Karenina (1877), about a married aristocrat who begins an ultimately tragic relationship with Count Vronsky.