During the latest tour of duty, members of the Prince of Wales's Company worked closely with Afghan security forces in Nahr-e-Saraj District to suppress insurgents and help the Afghan troops to take the lead themselves.
The battalion lost three members during the tour including Carmarthen-born Lance Corporal Lee Davies, 27, who grew up in Cardigan.
Lance Corporal Davies died after being hit by small arms fire while on working as part of a police advisory team in the Lashkar Gah district of Helmand province in May last year.
Major Ed Launders, Prince of Wales's Company Commander, said: "The tour in Afghanistan was extremely tough, but made much easier through the abundant support of the people of Wales which carried us through.
"It is a tremendous honour and privilege to march through Carmarthen and to display our gratitude."
More top news
It will be a dry night with clear spells for all of us, but the south-easterly wind will increase, becoming rather windy by morning.
Hundreds of campaigners are marching through the streets of Cardiff calling for the city's grassroots music venues to be protected.
People in Wales living with cancer face losing over £500 a month in income after diagnosis, according to Macmillan Wales.