Jens Peter Westergaard was born in Odense, Southern Denmark, Denmark, on 26 April 1914. His father owned a butcher shop on Nørregade street. During his childhood, he contracted the Spanish flu but made a full recovery.

His first wife, Gerda, died shortly after their 25th wedding anniversary. A year later, he met Igne, whom he would later marry. They were together for 17 years before her passing. Following the passing of his second wife, he entered a relationship with a woman named Nina. They never married but lived together for 17 years before her passing. He had at least one son, Hans.

Westergaard was first employed in Copenhagen’s accounting department at Politiken. Later, he served as the manager of public transportation in his city and supervised the transition from trams to buses in Odense. He played a pivotal role in the decision to discontinue the tram service in the city. He was featured in local newspapers on July 1, 1952, when the tram service was discontinued. He had intended to retire at the age of 67, but due to the absence of a successor, he continued working until he reached 70.

In 2020, he moved from Odense to Fredericia.

On 26 April 2024, he celebrated his 110th birthday, making him the first Danish-born man to achieve this milestone since Danish-American Christian Mortensen in 1992, as well as the first non-emigrant Danish man to become a supercentenarian.