Darren Bent insisted he had to leave Aston Villa after too many "slaps in the face".
Brighton defender Greg Halford has agreed to extend his loan deal from Nottingham Forest until the New Year.
Manager Peter Taylor has moved to bring in Hewitt with current right-back Michael Harriman away on international duty with the Republic of Ireland Under-21 squad.
Highly-regarded Hewitt, 19, signed for Ipswich from Macclesfield in the summer of 2012 but has not yet nailed down a regular first-team place at Portman Road, making 12 appearances.
He will now look to add to his experience at Priestfield, starting with Saturday's League One trip to Sheffield United.