Called Words + Pixels PR, Braund said the agency will "work with innovative B2B and B2C technology businesses, supporting them through launch, growth and scale".
The three founding clients are all in tech: Gruup, Digital Clipboard and Movewise.
Braund worked at PHA Group in two different spells, latterly as head of technology. His clients at the agency included Purplebricks, Happn and Lime.
His background also includes PR roles at the Ultimate Fighting Championship and record label Established 1954 Records.
Braund said: "I’m proud of everything we’ve done at PHA, and now I’m incredibly excited to launch Words + Pixels PR.
"Many startups and scaleups have the ideas to significantly disrupt their industry but aren’t able to work with some traditional agencies and therefore don’t receive the attention they deserve. We’ll be partnering with a range of exciting businesses in order to create a platform to help them grow and succeed."