Computing devices for automatic placement and arrangement of objects in computer-based 3D environments are disclosed herein. In one embodiment, a computing device is configured to provide, on a display, a user interface containing a work area having a template of a 3D environment and a gallery containing models of two-dimensional (2D) or 3D content items. The computing device can then detect, via the user interface, a user input selecting one of the models from the gallery to be inserted as an object into the template of the 3D environment. In response to detecting the user input, the computing device can render and surface on the display, a graphical representation of the 2D or 3D content item corresponding to the selected model at a location along a circular arc spaced apart from the default viewer position of a viewer of the 3D environment by a preset radial distance.