He will now return to the firm that he sold five years ago to take over the role of chairman. However, he said he did not want to outstay his welcome.
He said: "I'm looking to remain for three to five years. After that I will remain an investor, but in a passive, non-executive role. I don't want to force myself on the management."
He added that he wanted to widen ownership of the business to include existing and potential future managers.
Bucknall said he was not looking to overhaul the firm, which has 325 staff in seven offices, straight away, although he has changed the name back from Citex to Bucknall Austin.
He said: "It would be both practically and morally wrong to come in and say I was going to rebuild the business in 25 days."
Last week's deal did not include the group's property portfolio. Bucknall revealed that Bucknall Austin's offices were now occupied on leases of about six months.
Citex Project Services was the last part of the Citex Group to be disposed of; deals for the other two sections were concluded last summer.
The firm's facilities management division was sold to Carillion for £11.5m and its Asian division was sold to EC Harris. Both deals were finalised last August.
This left Citex Project Services as a private firm owned by shareholders, including venture capitalists Phoenix Equity Partners and Legal & General Ventures.
The original Bucknall Austin was bought by a management team in 1998. The deal was spearheaded by Oliver Jones, who has joined Carillion along with Citex's FM business.