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. 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. Google's partnership with Sony, with which it released a £200 set-top box, was poorly received.
That attempt followed an even earlier false start in 2010 when it launched Google TV, a service that was blocked by several TV networks, and suffered greatly from requiring consumers to buy expensive hardware. More recently, the orb-shaped Nexus Q device, announced last year, fell flat almost immediately - Google pulled it from sale in response to "feedback".
With Chromecast, Google is attempting to simplify its large-screen offering, focusing on streaming clips from services such as YouTube and Netflix via a far cheaper device.
