The Spaniard, who won the FA Cup with Wigan this season but also presided over a relegation campaign, succeeds David Moyes at Goodison Park.
Having led to club to a top-eight finish in nine of his 11 full seasons in charge, Moyes could prove a tough act to follow.
The Leeds-based firm also make Martinez a 9/1 chance to be August's Premier League manager of the month, while his new club are 5/1 to go winless in their first three games of the new campaign. The fixtures are announced on June 19.
The Toffees are also 9/4 to qualify for Europe next season and 10/1 to win any trophy.
Sky Bet's Chris Spicer said: "Most Everton fans seem to be giving Martinez their backing, but we believe they'll be more vulnerable to relegation than they were under David Moyes, cutting their price for the drop from 25/1 to 22/1.
"It's still a long shot but he's spent the large majority of his Premier League days in the bottom third of the table and we go 11/10 that he signs any player he suffered relegation with at Wigan during this summer's transfer window."