Former Shin Bet head Avi Dichter was expected to formally announce his joining Kadima Wednesday morning.
In recent weeks Dichter held intensive talks with Prime Minister Ariel Sharon over his position in the party; he was considered one of the leading candidates for defense minister, if Kadima wins the Knesset elections in March.
The party planned on completing its membership list by January 12, the same day as the Likud primaries.
According to Army Radio, Kadima's position in the polls has continued to rise, reaching a predicted 41 Knesset seats. On the other hand, Labor's prospects have dropped to 17.