The New Year has been celebrated on January 1 since the 46 B.C. According to the Julian calendar which was formulated by Emperor Julius Caesar.
Romulus created the early Rome calendar in the eight century B.C. The addition of Januarius and Februarius by Numa Pompilius caused the calendar to fall out of sync with the sun.
Emperor Julius Caesar with the help of some competent astronomers and mathematician created the Julian calendar which is in sync with the sun and has close accuracy with the Gregorian calendar.
January 1 was picked as the New Year day in order to honor Janus the god of beginning, who can see the future and past because of his two faces.
However, Christians celebrate New Year in order to thank God for the previous year. Pope Gregory XIII established 1 January as New Year in 1582.