By the time Berk graduated from high school in 1939, he was employing several area girls who made flies, silkworm gut, and cable wire leaders in their homes. The business soon outgrew Berk's parent's basement and living room. He expanded to the second floor of the local grocery store, using a tub filled with ice and a fan for air conditioning.

After attending the state university and serving in the Army Air Corps, Berk returned to Spirit Lake in 1945 to start Berkley and Company. The business focus was on its cable wire leaders. One evening, while reading Popular Science, Berk learned about a Connecticut company that was producing nylon-covered cable for sailboat rigging. After visiting their plant, he began to work on nylon-coated wire for use in fishing leaders. production began in Spirit Lake. Shortly after this, the distinctive Berkley heart logo was designed with the slogan "nylon leader with a heart of stainless steel."

Berk next became interested in extruding nylon monofilament fishing line. At that time, all nylon came from DuPont. After receiving a license from DuPont, Berk returned to Spirit Lake to begin work developing equipment to produce nylon. The initial extrusion equipment consisted of reclaimed washing machine wringers, bicycle wheels, and other homespun materials. Soon Berkley was marketing private brand mono as well as Dew Flex monofilament. Ongoing experimentation would soon yield the company's breakthrough innovation - Trilene.

In 1959, Berkley introduced Trilene at about the same time DuPont introduced Stren. To help introduce the new line, Berk sent out thousands of sample spools of line and asked store owners to have their best fisherman try it on a spinning reel. Fishermen loved the line and it began the successful launch of Berkley Trilene.

The next four decades were a time of great growth for the company. In the 1960's Berkley entered into the rod business, which lead to international expansion in the 1970's. Soft plastic baits made an appearance in the 1980's. The 1990's through today have seen significant technology improvements in all of the Berkley products. From the beginning, Berkley has committed significant resources to research and development - a continuing strategy that has resulted in countless product innovations, including Berkley Trilene, the Lightning Rod, PowerBait, FireLine, and more recently Gulp!? and Gulp! Alive.