Tā gānggāng zǒumǎshàngrèn, jiù kāishǐ dàdāokuòfǔ de gǎigé.
Right after assuming the position, he started reforming things drastically.
Tips
history
From Sun Guangxian's 《北梦琐言》 (Anecdotes from the Northern Dream, Song dynasty): 先以陈公走马赴任, describing an official 'riding a horse to his post.' In imperial times, riding to one's assigned post was the literal act; today the phrase is purely figurative for starting any new official role.
usage
Most natural for formal/leadership positions: managers, officials, directors. Don't use for an ordinary new employee; say 上班 or 入职 instead.