The city is named after Californio ranchero Ygnacio Martínez, having been founded on his Rancho El Pinole.

The beautiful, lush Alhambra Valley was probably a seasonal foraging “pantry” for the stable population of the Karkines Indians.

In 1824, the western side of Martinez, Alhambra Valley was included in the Rancho El Pinole Mexican land grant to Ygnacio Martínez.

In 1847, Dr. Robert Semple contracted to provide ferry service from Martinez to Benicia, which for many years was the only crossing on the Carquinez Strait.

[14] In 1860, Martinez played a role in the Pony Express, where riders would take the ferry from Benicia (particularly if they missed the steamer in Sacramento).

That area soon became known as Mococo, following the 1905 arrival of a smelting works, operated by the Mountain Copper Company (Mo Co Co).

A fourth refinery, built by the Shell Oil Company on land adjacent to the Martinez City limits, went online in January 1916.

The Shell Oil refining facility is still operational today (Currently owned by PBF Energy), maintaining the city's position as a significant petroleum processing center.

The Martinez–Benicia Bridge carries Highway 680 across the eastern end of the Carquinez Strait to Solano County.

The city is a densely built downtown valley threaded by Alhambra Creek and north of Highway 4.

Suburban areas stretch south of Highway 4 to join the neighboring city of Pleasant Hill.

[21] Martinez's location at the east end of the Carquinez Strait as it widens to Suisun Bay includes dramatic water views stretching to the Sierra range.

The maritime influence is much less significant than in other parts of the Bay Area that are closer to the Pacific, which causes very high daytime averages compared to San Francisco and Oakland in summer.

However, nights normally cool off significantly, which results in daytime highs around 87 °F (31 °C) and nighttime lows of 55 °F (13 °C) during July and August.

In December 2019, there was a flurry of reports from reliable sources including the Associated Press and the San Francisco Chronicle that the 161 year-old Martinez News-Gazette, one of the longest-running newspapers in California, may have to cease publication.

The newspaper did cease publication of a print edition effective April 2, 2020, but this was characterized as a temporary measure arising from a lack of advertising revenue.

This in turn arose as many local businesses were forced to suspended operations or even ceased to exist, when the area was under shelter in place regulations arising from the Coronavirus COVID-19 pandemic.

The newspaper plans to resume a full print edition when the local shelter-in-place restrictions are lifted.

Tri Delta Transit runs express service between Martinez and eastern Contra Costa County.