Despite a year-long slump in the online advertising market, Yahoo said its figures beat analyst expectations.
Mallett is leaving the company to "have greater flexibility for family and business interests," Yahoo said. The company is due to unveil a succession plan before his departure.
Yahoo reported revenues of $188.9m (£131.3m) for the quarter ended 31 December, compared to revenues of $310.9m in the fourth quarter of 2000.
The company also posted a consolidated net loss of $8.7m (£6bn) for the quarter, or a loss of $0.02 a share.
Net income for the fourth quarter totalled $16.7m (£11.6m), compared to pro forma net income of $80.2m for the year-ago quarter. The company said the pro forma figures exclude acquisition-related and restructuring charges, amortisation of intangibles and stock compensation.
The results of being tethered to a sinking advertising market were clear in the third quarter when Yahoo reported revenue that was almost half of what it was the year before. In an effort to stave its losses in future quarters, the Internet company cut 400 jobs as part of a restructuring effort that saw its 44 business categories reduced to six.
In recent months Yahoo shifted its market focus in an effort to diversify its revenue stream. In this vein, Yahoo finalised its $436m (£303m) purchase of recruitment site HotJobs.com in late December.