The dongle is plugged into a television's HDMI port, and allows users to stream media from smartphones, tablets and computers.
Launching immediately in the US, the device will cost $35 (£23). There is as yet no word on international launches.
Google also announced an upgraded Nexus 7 tablet, the first to run the new version of the Android system.Failed attempts
Chromecast is Google's latest attempt to gain ground in the television industry.
In 2012, Google faltered in its attempts to make a move into the living room, considered by many experts to be ripe ground for making large profits through advertising.