The Red Cross humanitarian movement has voted by a large majority to admit Israel, ending decades of isolation.
The new non-religious symbol can be used anywhere it is needed
The Magen David Adom has sought membership since the 1930s, but its red Star of David emblem is not accepted under the Geneva conventions.
The breakthrough came with approval of a third emblem, the Red Crystal, to identify relief and emergency workers.
A vote was held after Muslim states opposed Israel's membership over the status of land it occupied in 1967.
The same meeting of the international Red Cross and Red Crescent movement in Geneva approved membership for the Palestinian Red Crescent (PRC).
It had been excluded because the statutes only allow relief societies from sovereign states to join, but the rule was specifically modified to include the PRC.
It is hoped that the move to upgrade both societies from observer status will help engender better co-operation, say Red Cross officials.
The Red Cross and Red Crescent conference in Geneva had hoped for a universal consensus on Israel's admission, but the agreement almost collapsed when Syria raised objections over Israel's role in the occupied Golan Heights.
The issue was then put to a vote, in which 237 states and societies voted for the changes, with 54 voting against and 18 abstaining.
RED CROSS EMBLEMS
Used in conflict zones to protect medics and civil defence teams
Original symbol, reverse of Swiss flag, adopted in 1864
Red Crescent first used by Ottoman Empire in 1870s; formally recognised in 1929; used by 33 of 185 RC societies
Red Crystal can be used alone or in combination with recognised symbols
This gave the necessary two-thirds majority to modify the movement's statute and allow the change of emergency relief symbols.
An amendment demanding that the movement's rules apply to all the occupied territories - putting them under Palestinian, Lebanese and Syrian responsibility - was also rejected.
Correspondents say the Red Cross traditionally tries to work by consensus and to avoid potentially bruising ballot box confrontations among members.
The chair of the American Red Cross, Bonni McElveen-Hunter, said it would now pay about $45m in dues it has withheld since 2000 because of Israel's exclusion.
The Red Cross symbol - the reversal of the colours on the Swiss national flag - was adopted in 1863 when the organisation was set up to care for wounded soldiers.
Muslim countries objected to the use of the cross symbol, which is redolent of the Crusades in medieval times, and have used a crescent instead since the 19th Century.
The reversed Swiss flag was meant to signify neutrality
But until now, members have baulked at introducing a third symbol - a situation exacerbated by international opposition to Israel and its post-1967 occupation of Arab lands.
The new symbol, a red square at an angle on a white background, can be used by any relief teams in areas where there is sensitivity about Christian or Muslim symbols.
Israelis, including military medics, will be able to use the crystal by itself on a white flag. On their own territory - or with the agreement other states participating in UN operations abroad - they will be able to combine it with the star of David.
Under the Geneva conventions relief workers and ambulances bearing Red Cross-authorised symbols are protected under international law and must be granted free access to people in need of help.
In the past, RC officials have argued that having too many emblems could compromise their protection.