Helen Thomas, from Newcastle Emlyn, died aged 22 after being struck by a police vehicle in 1989.
A bench was dedicated in her memory in the town centre on Sunday.
Women from across the UK camped outside the Berkshire airbase during the 1980s and 1990s to protest at nuclear missiles being sited there.
Mayor Hazel Evans said the town council wanted to honour her memory and her commitment to peace.
The bench is by the town clock in Newcastle Emlyn.
Members of Miss Thomas's family joined the service along with prominent peace campaigners from Wales.
Folk singer Dafydd Iwan who wrote a song about Miss Thomas was also taking part.
Before the ceremony, Mrs Evans said: "Last year it was the 21st anniversary of her death and there was a service at Greenham Common.
"She was born and went to school in Newcastle Emlyn and her family still have a business here.
"We felt it was appropriate to remember her fight against nuclear weapons."
Following her death, Miss Thomas's family challenged the verdict of accidental death at the High Court but the judge refused to re-open the inquest.
The first Cruise missiles were delivered to Greenham Common in November 1983. The last one was removed in March 1991.
During the height of the protests, thousands of women blocked the entrances to the base, cut through perimeter fences and formed human chains around the site.
The airbase was closed in 1993 but the peace camp remained until 2000.
A memorial has been unveiled to a Carmarthenshire woman who died while taking part in the Greenham Common peace protests.