Tulchan, founded by Andrew Grant, beat Gavin Anderson in a final two-way pitch to secure the brief, replacing six-year incumbent GCI Financial.
Candover said the decision to repitch followed a number of departures at the agency, including the firm's original key account handlers.
GCI UK chief executive Adrian Wheeler took over direct control of the financial division last August following the surprise departure of financial CEO Philip Robinson - a move that followed a number of senior staff departures and a raft of redundancies (PRWeek, 16 August 2002).
Candover marketing director Helen Walsh conducted a marcoms review last year, which led to a PR overhaul.
'It was thought that we weren't using media relations as effectively as we should be,' she said.
The group has been the centre of attention this week following reports that it was part of a consortium of venture capitalists to approach Daily Mirror parent Trinity Mirror at the end of last year.
Candover and fellow VC Cinven also last week entered exclusive takeover negotiations with British bingo and casino giant Gala in a deal which would value the firm at up to £1.3bn.