Buffalo Bills fans have belatedly got their Christmas wish

Mularkey was handed his big break after spending 10 years as an assistant coach at the Pittsburgh Steelers.

Mularkey takes over from Gregg Williams, who struggled through three disappointing seasons in Buffalo.

Smith succeeds Dick Jauron who was fired after leading the Bears to their fourth losing season in five years.

Meanwhile, the New York Jets have extended the contract of coach Herman Edwards for two more National Football League campaigns.

The 42-year-old Mularkey has never held a head coaching position at any level, but has transformed Pittsburgh into one of the NFL's top ranked offences.

Smith, 45, becomes the 13th head coach of one of the NFL's original franchises.

"I know about the tradition of the Chicago Bears and I know the passion that the fans have for the organisation here," Smith said.

Smith spent three seasons as defensive co-ordinator in St Louis, helping the Rams reach the 2002 Super Bowl.

Both Mularkey and Smith will officially be introduced as head coaches at news conferences on Thursday.