Kamaishi Station opened on 17 September 1939. The Kamakishi Line began operations from 11 October 1944. The station also became a terminal station for the Miyako Line on 27 February 1972. This line was privatized on 1 April 1987, becoming the Sanriku Railway South Rias Line. Kamaishi Station was absorbed into the JR East network upon the privatization of the Japanese National Railways (JNR) on 1 April 1987. The 2011 Tōhoku earthquake and tsunami on 11 March 2011 destroyed much of the tracks and many stations of the Yamada Line between Miyako and Kamaishi. In February 2012, JR East officially proposed that this section of the Yamada Line be scrapped and the right-of-way used as a bus rapid transit (BRT) route but this decision was subsequently overturned and the line restored pending transfer to the Sanriku Railway. On 23 March 2019, the Yamada Line section from Miyako to Kamaishi was reopened and transferred to Sanriku Railway. This joined up with the Kita-Rias Line on one side and the Minami-Rias Line on the other which together constitutes the entire Rias Line. Accordingly, this station became an intermediate station of the Rias Line.