In announcing the new agreement, the UK government said it was the only country in the world to have secured a zero percent tariff rate for pharmaceutical shipments.
European officials have previously said they believed their drugs exports would be protected by terms agreed over the summer, which would cap tariffs on most goods at 15%.
It follows pressure on the government after the cancellation or pause of several large pharma investments in the UK over the last 18 months, as firms shift attention to the US.
In mid-September, British pharmaceutical giant GSK pledged to invest $30bn (£22bn) in research and manufacturing in the US over the next five years.
A week before GSK's US investment announcement, US pharmaceutical company Merck - which is called MSD in Europe – revealed it was scrapping its planned £1bn expansion of its UK operations.
Shortly after, AstraZeneca also announced it was pausing a planned £200m investment in a Cambridge research facility. In July, AstraZeneca said it would invest $50bn on medicine manufacturing and research and development in the US.
William Bain, head of trade policy at the British Chambers of Commerce, said he was pleased to see that the protections from US tariffs that UK officials had promised earlier this year had been delivered.
"This deal is a real win. It will promote exports, boost investment, and enhance UK competitiveness as a production and innovation base for world-leading medicines and treatments," he said.
US pharmaceutical company Bristol Myers Squibb said it now anticipated being able to invest more than $500m over the next five years in areas including research, development and manufacturing.
"This agreement is a sign of progress and one that creates an environment conducive to our continued presence in the UK," chief executive Chris Boerner said.