The First Siege of Constantinople (Istanbul) had lasted for four years between 674-678 during the reign of Muawiyah I. This siege came at the back of the Battle of the Masts which resulted in the Arab victory.
There was another siege of Constantinople by the Arabs which is known as The Second Arab Siege of Constantinople in 717–718 but it was during the first siege when many sahaba traveled to Constantinople. During the this period of four years (674-678) many sahaba took their last breath outside the city walls of Constantinople.
Very little is known about the lives of those buried here; some of them are barely known by names. According to the Research Centre for the Islamic History, Art and Culture, in Istanbul, the bulk of information provided about their lives is through a major booklet by a Turkish writer: Professor Dr A. Suheyl Unver's Istanbulda Sahaba Kabirleri (The Graves of the Sahaba in Istanbul), and few notes written about them in Turkish.
The graves of Sahaba are spread all over Istanbul. But a majority of them are situated close to the area of Eyub Sultan and Avansarayi. Of the well-known ones that are here, Hazrat Ayub (in Turkish spelled as Eyub).

I managed to see 24 graves of Sahaba in Istanbul but remaining 4 I was unable to find due to lack of local knowledge. Photos of the 24 graves which I have visited can be found here.

1- Hazrat Eyub
Location; Eyüp Sultan Camii
Address; Merkez Mh. Kalenderhane Cd. No:1, 34050 Eyüp
Hazrat Eyub (Ayub) Ensari's (for Ansari in Turkish) shrine exists in the courtyard of Sultan Eyub Camii (Mosque), Sultan Eyub area.
His shrine is a famous pilgrimage place for people all over Turkey and other parts of the world.  The shrine is believed to have been venerated by Byzentines long before the Ottoman rule was established in Istanbul.

When Muhammad arrived in Medina from Mecca, all of the inhabitants of the city offered to accommodate him. He decided instead to allow his camel to walk where it chose and to stay at whomsoever's house it stopped. The camel of its own accord, stopped at the hose Abu Eyub al-Ansari.
Hazrat Eyub passed away in 672.

2- Hazrat Abu Derda
Location; Zal Mahmud Pasha Mosque
Address; 34 Zalpasa Cd. Eyup
He is also known as Eby Derdag, his tomb is a short distance away from the famous Eyub Mosque. Derda was the name of his daughter hence he is called Abu Derda. Some historians belive that Abu Derda died in Damascus in 652.

3- Hazrat Edhem (Ahdem)
Address; 11 Abdurrahman Serefbey Cd. Eyup
As per info at the grave of this sahaba his name is  Halid/Khalid and the year 46/666. Al-?abari mentions that ‘Abd al-Ra?man, the son of the famous Khalid ibn al-Walid, possibly led a campaign against the Byzantines in 46H before being killed by poison later that same year.

4- Hazrat Hayreddin (Khariddin)
Location; Arpaci Hayrettin Cami
Address; 1 Arpaci Hayrettin Sk. Eyup

5- Hazrat Abdulvedud
Location; Ya Vedüd Cami
Yavedut Cd. Eyup(opposite the Vedud Mosque)

6- Hazrat Kaab
Hazreti Kab Mescidi
Address; A
yvansaray Cd. (at the back of Haci Hüsrev Cami)

7- Hazrat Humeyd bin Bekir
Haci Hüsrev Cami
Address;  Ayvansaray Cd.

8- Hazrat Abu Seyb el-Hudri
Haci Hüsrev Cami
Address;  Ayvansaray Cd. Eyup
He is also known as Abu Seybeti or Shahbat. This saba is also the foster brother of the Holy Prophet. Abu Seybeti died in 74AH.

9- Hazrat Ahmed el-Ensar
Haci Hüsrev Cami
Address;  Ayvansaray Cd. eyup

10- Hazrat Muhammed el-Ensari
111 Ayvansaray Cd. Eyup

11- Hazrat Jabir bin Abdullah
Location;  Jabir Camii
9 Çember Sk. Fatih
His father was Abdullah bin Amr. Hazrat Jabir is a famous warrior Shahbi who participated in all battles alongside the Holy Prophet. As mentioned on the introductory tablet about his short life sketch, he was born 16 years before the Hijrat. As a great warrior he participated in a total of 19 battles, including of Badr and Uhad. He served as an adviser to the four Caliphs on war matters. Soon after the martyrdom of Hazrat Ali he moved to Syria. Later on, he is believed to have migrated to (Constantinople). As the record shows he was martyred in a battle in Istanbul in 697AD.

12- Hazrat Abuzer Gifari
Hazreti Ebuzergifari Cami
Adress; 7 Albayrak Sk. Fatih

13- Hazrat Hafir
Location; Egri Gate
1 Egrikapi Cd. Avansaray, Fatih

14- Hazrat Abdul Sadiq bin Amir
Location; Egri Gate
Address; 1 Egrikapi Cd. Avansaray, Fatih (close to Hazrat Hafir's grave)

15- Hazrat Su'be or Hazrat Sabe
Location; close to Egri Gate
Address; Sishane Caddesi in Avansaray

16- Hazrat Abdullah el-Hudri
Address; at the end of Kandilli Türbe Sk. in Ayvansaray

17- Hazrat Abu Said el-Hudri (Abdullah el-Hudri)
Location; Edirnekapi.
Kariye Türbesi Sk, close to Chora Museum
The record available about his life shows that he entered Istanbul with Islamic troops at the age of 15. He participated in all battles fought against Romans. He died in 666AD.

18 &19 - Hazrat Hassan and Husayin
Location; Edirnekapi
Salma Tomruk Cd. Fatih
he two brothers are buried in Salmatomruk Pashamam, Hassan huseyin yokusu (downhill). The graves are surrounded by a compound built with an entrance. They are believed to have reached the area with Hazrat Eyub when very young, and were martyred during the siege of Constantinople.

20- Hazrat Amr bin As
Location; Yeralti Camii
Address; Kemankes Karamustafa Pasa Mah., Kemankes Cad. 34425 Beyoglu
Some historians believe that this grave belong to the famous Muslim general Hazra Amr bin al-As who conquered Egypt in 640 but its is highly unlikely that he is buried here believing that he was born in 585 and he served as governor of Egypt(642–644) and (657–664). He passed away in Fustat (old Cairo).

21- Hazrat Wahb
Location; Yeralti Camii
Address; Kemankes Karamustafa Pasa Mah. Kemankes Cad., 34425 Beyoglu

22- Hazrat Sufyan ibni Ubeyne
Location; Yeralti Camii
Address; Kemankes Karamustafa Pasa Mah. Kemankes Cad., 34425 Beyoglu

23- Hazrat Mesleme bin Abdul Malik
Location; Arab Camii Mosque
Address; Arap Cami Mahallesi, 34420 Beyoglu

24- Hazrat Abdul Rehman Sami
Location; 200m from the Hagia Sophiya
Address; Kabasakal Cd. No:1, Sultanahmet, Fatih

25- Hazrat War bin Abdullah
Location; Hoca Kasim Camii
Address; 15 Sultan Çesmesi Cd. Fatih

26- Hazrat Abdullah Ansari
Location;  Edirnekapi
Address; Salma Tomruk Cd. Fatih

27- Hazrat Husam bin Abdullah
Location;  Edirnekapi
Address; Salma Tomruk Cd, Fatih

28- Hazrat Abdul Rauf Samdani
Location; Close to the grave of Baba Jaffer
Address; TBC