The son of Archon Elizabeth Steiner, Eric assumed control of the Commonwealth without opposition following her death in her sleep in 2895. Eric inherited a realm under siege as House Kurita's long-running offensive against the Commonwealth continued, and while the Lyran Commonwealth Armed Forces inflicted heavy damage upon the Draconis Combine Mustered Soldiery, it was unable to prevent the loss of Imbro, Buckminster, Moore, Phalan, Sakhalin and Orestes. The on-going conflict with the Combine and the Free Worlds League would also overshadow one of the greatest natural disasters in Lyran history, the Beta Regulus Tragedy of 2901, with Eric and the entire Lyran realm barely able mourn the four million people killed as the fighting continued unabated.  
Unfortunately as the Third Succession War dragged on, the future outlook for the Commonwealth looked increasingly dire with the LCAF experiencing severe manpower shortages, with few LCAF regiments boasting even 70 percent of their full strength. In response, Eric modified the Military Services Acts in 2908, reducing the minimum age of conscription to sixteen, increasing the duration of service to five years and tightening up rules for valid exemptions from service. Despite its vital need, Eric's decision was highly unpopular among the civilian population of the Commonwealth, even on worlds directly threatened by the Combine. Farming worlds particularly resented the changes, citing their increasing need for labor in the face of the steep decline in technology of the era. Demonstrations and riots erupted on numerous worlds, but Eric had the support of the nobility who understood the need for the new measures, allowing him to weather the political backlash.
As badly-needed recruits finally brought many line regiments back to full strength, Eric revealed to the Lyran High Command his plan for Operation Freedom, an offensive intended to recapture Federation of Skye worlds and reclaim vital industries from the Combine. After Tamar itself was placed at risk when the worlds of Kobe and Sevren fell in 2912, the High Command quickly approved the plan and Operation Freedom was officially launched in February 2913. Eric personally led the Third Royal Guards in the recapture of Freedom itself during the opening of the offensive. Through skilful manoeuvring and strong attacks, the Third was able push the bulk of the 6th Sword of Light into a closed valley, blocking their escape as the Third Royal's artillery and aerospace support pounded the Kurita forces and allowing the Lyran 'Mechs to easily mop up the remainder.  
Death and Legacy
The news of the Third Royal Guards victory was quickly overshadowed when Archon Eric Steiner died in its immediate aftermath, unwittingly straying into a field of unexploded mines in the valley and killed instantly when his Zeus toppled head-first onto a live vibrabomb.
Simon Borge-Steiner is described as Eric's eldest son, and in conjunction with his sister Tatyana Steiner as Eric's two grown children. It is possible therefore that Eric had one other son, who was not of age by the time of Eric's death.
|β||I didn't expect to be a very popular leader. But I assumed I would be the unpopular leader of the Commonwealth and not 300 separate, selfish worlds.||β|
|— Archon Eric Steiner, on objections to his revision of the Military Services Act, in Royal Court Transcripts Year 2909, Commonwealth Historical Press, 2909|
|Archon of the Lyran Commonwealth
| Succeeded by|
- Handbook: House Steiner, p. 97, "Lyran Leadership Profile"
- House Steiner (The Lyran Commonwealth) pp. 70-71 "History - The Third Succession War - Calling All Citizens"
- Handbook: House Steiner, pp. 46-48 "History of the Lyran Alliance - Third Succession War (2866-3025) - The Combine Front - The Beta Regulus Tragedy"
- House Steiner (The Lyran Commonwealth) p. 71 "History - The Third Succession War - The Cost of Freedom"
- Handbook: House Steiner pp. 48-49