The midfielder, 30, was not part of Saturday's matchday 18 for the 1-1 draw against York and has now linked up with Blue Square Bet Premier promotion chasers Harriers in order to be closer to his family.
Jackman scooped Gillingham's Player of the Year award last season following 44 appearances in which he scored five times.
He has enjoyed two separate spells at Priestfield, first joining in 2005 before leaving two years later for Northampton and then returning in the summer of 2009. He made a total of 168 appearances and scored nine goals.
Manager Martin Allen told the club's official website: "We received last week an offer from Danny Jackman's representatives for him to go to Kidderminster on an 18-month contract.
"Danny has a young family and is from the Worcester area and he felt this was too good an opportunity to turn down and wanted to go.
"Danny is a top professional, a really good bloke and I'm sure everybody will have enjoyed Danny Jackman at Gillingham Football Club on and off the field."