The phrase "a key liaison" is correct and usable in written English.
You can use it when referring to an important person who facilitates communication or cooperation between different parties or groups.
Example: "In our project, Sarah serves as a key liaison between the marketing and development teams to ensure smooth collaboration."
Alternatives: "a crucial intermediary" or "an essential contact".
Bremberg has served as a key liaison with Brennan.
He was a key liaison between the council and a UK-funded agency, Adam Smith International.
He would serve as a key liaison between the defense secretary and the top brass.
Jones is the voice and pulse of the defense and a key liaison for players with Coach Dick Vermeil.
He served as a key liaison to the president's conservative base and the custodian of his campaign promises.
Priebus, who has been named chief of staff, is a longtime friend of Ryan's and is widely seen as a key liaison for Trump on Capitol Hill.
The Co-ordinator, as noted above, is a clinical expert in burn and disaster management, and is the key liaison between the Australian Government, national health disaster planners, burn clinicians, and, most importantly, the Australian public, in the event of AUSBURNPLAN activation.
He therefore was the key liaison man between the Government and the army, and head of the presidency's special intelligence network.
The key liaison between merchants, agents, banks and the underwriting team, Trish provides extensive support to serve their unique needs and achieve optimal results for all accounts.
Electronic records are searched by identified key liaison staff in the practices and clinics.
He was also closely involved since the beginning in the establishment of the United Nations Global Geospatial Information Management (UN-GGIM) programme and acted as the key liaison between the Division and the UN Economic and Social Council (ECOSOC) during the negotiations of the UN resolution that formally launched UNGGIM in 2011.
