Born around 1526, Ikoma Chikamasa served Oda Nobunaga and later Toyotomi Hideyoshi, campaigning across the country. After Hideyoshi's Kyushu campaign in 1587, he was granted the whole of Sanuki Province and entered Takamatsu. Choosing a site facing the Seto Inland Sea, he built Takamatsu Castle in 1590 as a "water castle" whose moats were filled directly with seawater. A 1595 cadastral survey fixed his holdings at 126,200 koku. In 1597 he began construction of a satellite castle at Marugame's Kameyama hill, completing most of the fortress within six years. In his later years he served the Toyotomi government as one of the "Three Chunin" alongside Nakamura Kazuuji and Horio Yoshiharu. He retired in 1602, passing the domain to his son Kazumasa, and died in 1603. As the daimyo who laid the foundations of Kagawa's two premier castles — Takamatsu and Marugame — he remains a defining figure in the region's history.

A moderate, conciliatory figure whose selection as one of the Toyotomi government's "Three Chunin" reflects a reputation for administrative skill and mediation. He is also credited with a keen eye for choosing strategic, sea-facing castle sites.

He laid the foundations of two of Kagawa's premier castles: Takamatsu, one of Japan's Three Great Water Castles, and Marugame, home to what are said to be Japan's tallest stone walls. Both remain celebrated National Historic Sites today.