The 29-year-old has penned a two-year contract at One Call Stadium.
Stags’ boss Nigel Clough said: “Oli will add a real presence in both penalty areas, something which we missed last season, both defensively and offensively.
“He’s an unselfish player and his assists ratio is very good, but his presence in both penalty areas is the main reason why we’re signing him.
“He’s been playing in teams who have competed towards the top end of League One in the last few seasons and we’re excited to add him to our existing line-up of strikers.”
Hawkins began his career in non-league, flourishing in front of goal with North Greenford United, Hillingdon Borough, Northwood, Hemel Hempstead Town and Dagenham & Redbridge.
In the summer of 2017, Portsmouth secured his services, where he went on to score eight goals in 26 starts and nine substitute appearances as Pompey finished eighth in League One.
The following season, Hawkins netted 10 goals in 36 starts and 12 substitute outings, while also scoring the clinching penalty in an EFL Trophy Final victory against Sunderland at Wembley.
The Londoner was then snapped up by Ipswich Town in August of last year where he was sidelined with a knee injury while there was a change of manager and new boss Paul Cook has allowed him to leave, despite having another year of his deal to run.
Hawkins is Stags’ third new face this summer following the arrivals of striker Danny Johnson and defender Elliott Hewitt while midfielder Stephen Quinn has signed on a permamant basis after a successful loan spell last season.