Clarksons, which has interests in broking, financial services and research around the world, said the move will boost its existing port and agency operation. It now expects to tender for larger offshore and renewable contracts.
The market reacted by sending Clarksons' shares up 47p to 2063p.
The deal marks the end of family ownership for Gibb, which was established in 1933, with listed Clarksons having bought the business from director Iain Clark, fellow Clark family members and a number of staff.
Mr Clark and the employee owners will stay with the group, based in Aberdeen's King Street. Gibb has a Ghana office and had 24 staff in its last financial year.
It was not disclosed whether the selling parties received any windfalls as a result of the deal.
The new owner, which dates back to 1852, paid an initial consideration of £5.7m in cash and £0.5m in 22,645 ordinary shares in Clarksons on completion of the deal.
A further cash payment of £1.7m may be payable between now and April 2014 arising from balance sheet adjustments, with an additional £3m in cash deferred and payable within two years.
The value of the deal could swell by an extra £1.8m if certain performance targets are met within two years of the deal completing. This sum is payable by February 2016.
London-based Clarksons said Gibb, which has gross assets of £9m, will boost its pre-tax profits by £2m before costs relating to the acquisition are taken into account.
In its most recent financial year, Gibb saw earnings before tax of £1.8m and turnover of £9.24m for the year to March 31. Gross assets for the period were £6.5m.
In its interim results announced on August 19, Clarksons reported trading in its current year was in line with expectations. Revenue for the six months ended June 30 was reported at £89.1m, compared with £88m for the same period in 2012, with profits before tax, exceptionals and acquisition costs unchanged at £10.8m.
Andi Case, chief executive of Clarksons, said: "We are excited to welcome Gibb Tools into Clarksons. The acquisition allows Clark Port Services to further extend its port and agency client offer into the important tool supply market, bringing with it a wealth of complementary client relationships and allowing us to tender for larger contracts.
"In turn, we believe Clarksons will bring international scale to Gibb Tools as we integrate their business across our global network."
Responding to the acquisition, house broker Panmure Gordon retained its recommendation to buy the Clarksons stock.