Westcoast claims it has sold over 250,000 cloud service provider (CSP) seats through partners in the UK.
The distributor has more than doubled its total in under a year after breaking the 100,000 barrier in October 2016.
Mark Davies, cloud services director at Westcoast, said the firm has reached the milestone ahead of its competitors.
"Business is absolutely booming for Westcoast and its CSP partners," he said in a statement. "We've come a long, long way in two short years.
"Despite the fact we started selling cloud services after most of our competitors, we were the first distributor to pass 100,000 seats and now we've accelerated away to reach another big milestone ahead of anybody else in the UK.
"Our strategy of pursuing deep engagement with selected partners that are focused on properly activating and supporting their end-customers is really paying dividends."
Earlier this year Microsoft launched its Cloud Development Programme, focused around Microsoft Azure.
On Westcoast's 250,000 milestone, Microsoft's UK Office business lead Angela Evans said: "Companies of all sizes are undergoing a digital transformation, driven by incredible advances in cloud computing, the proliferation of apps and devices, and the ability to interpret more data to make better decisions.
"It's great to see Westcoast break through another significant milestone. Reaching 250,000 cloud seats [is] further testimony to the unprecedented growth we are witnessing."
Westcoast reached the landmark figure on Tuesday, following an order from London-based Keybridge IT.
Andy Hinxman, director of IT services at Keybridge IT, said: "Westcoast has helped transform our company by enabling us to act quicker and work more effectively.
"The professionalism provided by the Westcoast team means we can offer our clients an even better service.
"We've been able to add more services to our portfolio, move into new markets and take advantage of emerging revenue opportunities. As a result, we've seen an increase profits which we have reinvested in staff training and incentives."
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