I have read A Year in the Life of Ancient Greece by Philip Matyszak. It follows the life of multiple characters:

• a farmer from Elis
• a diplomat
• a runaway slave
• a sprinter from Neapolis
• a teen girl preparing for marriage
• a builder/architect
• a lyre player The book is about 260 pages long and contains a lot of interesting facts while having a story.

Mage Errant by John Bierce has a main warlock character who pacts with a greater power. There are other ways of pacts as well that feature throughout the series. This is one of my favorite all time series, particularly for the main group of teenagers who support each other no matter what. The magic system is great and worldbuilding starts to shine as the series progresses.

Some recommendations for novels based on Greek mythology (though I haven't read them yet):

• Soldier of the Mist series by Gene Wolfe
• Troy trilogy by David Gemmell

I love Madeline Miller’s books set in Ancient Greece. The Song of Achilles is set during the Trojan War, and Circe explores several Greek myths through Circe’s perspective. The Song of Achilles definitely made me tear up at some points, and really made the inclusion of Patroclus and Achilles in the game Hades hit way harder for me.

Troy by Stephen Fry

Now, I haven't finished the book, in fact I have only read maybe 30 pages so far, but Ilium by Dan Simmons could be a fit. It features a character that is tasked by a divine entity to explore the events of Homers Iliad. It is Sci-fi though and I am not sure if the book will keep this characters storyline in Greece or even under this pact.

If someone has actually read the whole book (series) please chime in!