The new division, Good Live, has been set up to "help brands populate culture by creating entertaining brand experiences from installations and pop-ups to shareable content".
Day was formerly group account director at Taylor Herring, and before that account director at Mischief PR.
Good Relations chief executive Richard Moss said: "Whilst the power of digital communications continues to grow, we are seeing increasing demand from consumers for meaningful physical experiences. Kat is a hugely talented and inventive communications professional, and we’re delighted to welcome her into our fast-growing team."
The agency was incorporated into VCCP Partnership in 2015 after the brands' parent company Chime was acquired by a private equity-led consortium.
Good Relations was listed at number 48 on PRWeek’s most recent UK Top 150 Consultancies report, with revenue of £6.4m in 2016.
A version of this article was first published on www.prweek.com