Axelrod, who joined WPP from McKinsey & Company where she was a principal consultant, was named in April as Brooks' replacement. However, at the time she was not named to the WPP board of directors.
It is unclear at the time why this was so, although it was seen as an unusual move.
Brooks has just completed a 12-month gardening leave period, after resigning from WPP last year to take up the post of human resources at the Interpublic Group of Companies.
Axelrod is responsible for the recruitment, development and retention of WPP's staff worldwide and has a brief to work closely with WPP's operating companies.
At the time of her appointment, WPP chief executive Sir Martin Sorrell said: "The critical differentiator in our industry is the quality of our people. Beth's business strategy, personnel management and organisational background will add leadership and insight to our talent-building efforts."
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