Thorpe has been with the firm since 2004, joining as head of UK advisory sales before being appointed to head up UK advisory sales in August.
Prior to this he held positions at Newton Asset Management and JP Morgan. He is expected to join another firm later in the year.
Last week Chris Rice announced he was to leave his role as head of pan European equities, being replaced by Julie Dean. He will remain at the firm until July to ensure a smooth transition.
The £424m deal was announced in March this year, and is due to complete on 2 July, subject to regulatory approval.