The 27-year-old "Coronation Street" star, who is engaged to marry Mark Wright, has previously ranked second in 2014 and fourth in 2013 in FHM survey, reported the Daily Mirror.
She is closely followed by Kendall Jenner, who makes her top ten debut, up 29 places, and last year's winner Jennifer Lawrence, who has drops two places to third.
Keegan first entered the list in 2010 at number 30 and after years of winning sexiest soap star she has finally nabbed the big prize.
American pop star Ariana Grande jumps a huge 71 spots this year to take up sixth position ahead of "The Wolf of Wall Street" actress Margot Robbie at seven.
Lucy Mecklenburgh is a non-mover at eight and "Game of Thrones" star Emilia Clarke is at nine.
Rounding off the top ten is Kelly Brook, who made her first entry in 1998 and went on to take the top honours in 2005, she is not the most featured Brit in the top 100 with 18 entries.