Pippa is currently Deputy Political Editor at The Guardian. She will join the Mirror politics team in December.
Andrew Gregory is departing for a new role at the Sunday Times.
Mirror Editor Alison Philips said: "We are absolutely delighted Pippa is joining our brilliant political team in such a key role - I know she will be a fantastic ambassador for the Mirror brand."
Pippa Crerar tweeted: “It feels particularly special as my first ever Fleet Street job back in 2000 was at the Daily Mirror. Loved the paper then, love it now. Can't wait to get started.”