Day will take over from Shane Richmond, who was named as editorial head of a newly created technology team last month, a press release from the group has confirmed.
She will oversee the Telegraph's blogs and reader community MyTelegraph.
Day joined the Telegraph's communities team in May 2007 and has written a photography blog for the site since May 2008.
She has been social networks content editor since October 2008.
Prior to joining the title she was a reporter for a local newspaper in California and completed a postgraduate diploma in newspaper journalism at City University.