Julie-Anne Wood started her career in her hometown of Milford Haven in 1999.
She has now become the Maritime and Coastguard Agency's head of maritime operations and oversees the co-ordination of search and rescue around the UK coast.
Up until now the role has always been held by a man.
Ms Wood, who started out as a part-time coastguard watch assistant, said what once had been a male-dominated industry had changed.
"[It's] very different these days. The Maritime and Coastguard Agency has incorporated women in everything they do," she said.
"In my experience, there have been no restrictions."
Of her new position, she added: "'It's a huge responsibility and a position that I'm very honoured to hold."
Before she became a coastguard, Ms Wood ran her own business providing safety training to fishermen and merchant seamen in Wales.
When an opportunity to become a coastguard watch assistant came up, she took the job and said she "never looked back".
Over the next nine years she climbed the ranks and now has one of the most senior roles in HM Coastguard, heading up the National Maritime Operations Centre in Fareham, Hampshire, and the 10 Coastguard Operations Centres around the UK.
A coastguard from Pembrokeshire has made history by becoming the highest-ranking woman in Her Majesty's Coastguard.